System including a buffered memory module

ABSTRACT

According to embodiments, a system includes a master device and a first memory module having a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices that operate in first and second modes of operation (bypass mode). In a first mode of operation, a first memory module provides read data from the plurality of integrated circuit memory devices (via a integrated circuit buffer device) on a first signal path to the master and a second memory module simultaneously provides read data from its plurality of integrated circuit memory devices (via another integrated circuit buffer device on the second module) on a third signal path coupled to the master device. In a second mode of operation, the first memory module provides first read data from its plurality of integrated circuit memory devices (via the integrated circuit buffer device) on the first signal path and second read data from its plurality of integrated circuit memory devices (via the integrated circuit buffer device) on a second signal path that is coupled to a second memory module. An integrated circuit buffer device in the second memory module then bypasses the second read data from the second signal path and provides the second read data on a third signal path coupled to the master device.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 11/236,401 filed on Sep. 26, 2005 (still pending).

FIELD OF THE INVENTION

The present invention generally relates to integrated circuit devices, high speed signaling of such devices, memory devices, and memory systems.

BACKGROUND

Some contemporary trends predict that processors, such as general purpose microprocessors and graphics processors, will continue to increase system memory and data bandwidth requirements. Using parallelism in applications such as multi-core processor architectures and multiple graphics pipelines, processors should be able to drive increases in system bandwidths at rates some predict will be doubled every three years for the next ten years. There are several major trends in dynamic random access memory (“DRAM”) that may make it costly and challenging to keep up with increasing data bandwidth and system memory requirements. For example, transistor speed relative to feature size improvements in a given DRAM technology node, and the rising costs of capital investment required to move DRAM technology to greater memory densities for a given DRAM die adversely affect the rate at which DRAM technology can keep pace with the increasing data bandwidth and system capacity requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

FIG. 1 illustrates a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices;

FIG. 2 illustrates a memory module topology having a split multi-drop control/address bus;

FIG. 3 illustrates a memory module topology having a single multi-drop control/address bus;

FIG. 4 illustrates a memory module topology that provides data between each integrated circuit buffer device and a memory module connector interface;

FIG. 5 illustrates a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices with an integrated circuit buffer device for control and address information;

FIG. 6 illustrates termination of a control/address signal path in a memory module topology of FIG. 5;

FIG. 7 illustrates termination of data signal paths in a memory module topology of FIG. 5;

FIG. 8 illustrates termination of a split control/address signal path in a memory module topology of FIG. 5;

FIG. 9A illustrates a top view of a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices;

FIG. 9B illustrates a side view of a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices;

FIG. 9C illustrates a bottom view of a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices;

FIG. 10 is a block diagram illustrating a topology of a device having a plurality of integrated circuit memory dies and an integrated circuit buffer die;

FIG. 11 illustrates a multi-chip package (“MCP”) device having a plurality of integrated circuit memory dies and an integrated circuit buffer die;

FIG. 12 illustrates a device having a plurality of integrated circuit memory dies and a buffer die;

FIG. 13 illustrates a device having a plurality of integrated circuit memory devices and a buffer device that are disposed on a flexible tape;

FIG. 14 illustrates a device having a plurality of integrated circuit memory dies and a buffer die that are disposed side-by-side and housed in a package;

FIG. 15 illustrates a device having a plurality of integrated circuit memory dies and a buffer die that are housed in separate packages and integrated together into a larger POP device;

FIG. 16 illustrates a memory module topology including a serial presence detect device (“SPD”);

FIG. 17 illustrates a memory module topology with each data slice having an SPD;

FIG. 18 is a block diagram of an integrated circuit buffer die;

FIG. 19 is a block diagram of a memory device;

FIGS. 20A-B illustrate signal paths between memory module interface portions and a plurality of integrated circuit buffer devices;

FIGS. 21A-D illustrate memory system point-to-point topologies including a master and at least one memory module (shown as buffer 101 a) having a plurality of integrated circuit memory devices;

FIGS. 22A-C illustrate memory system daisy chain topologies including a master and at least one memory module having a plurality of integrated circuit memory devices;

FIGS. 23A-C and 24A-B illustrate memory system topologies including a master to provide control/address information to a plurality of integrated circuit buffer devices;

FIGS. 25A-B illustrate memory modules having different sized address spaces, or memory capacity;

FIGS. 26A-B illustrate a memory system including a master and two memory modules operating during a first and second mode of operation (bypass mode);

FIG. 27 illustrates a memory system including a master and at least four memory modules;

FIGS. 28A-B illustrate memory systems including a master and four memory modules operating during a first mode and second mode of operation (bypass mode);

FIG. 29 illustrates a bypass circuit;

FIGS. 30A-B illustrate timing diagrams for an integrated circuit buffer device;

FIG. 31 illustrates a method to levelize memory modules according to an embodiment.

DETAILED DESCRIPTION

According to embodiments, a system includes a master device and a first memory module having a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices that operate in first and second modes of operation (bypass mode). In a first mode of operation, a first memory module provides read data from the plurality of integrated circuit memory devices (via an integrated circuit buffer device) on a first signal path to the master and a second memory module simultaneously provides read data from its plurality of integrated circuit memory devices (via another integrated circuit buffer device on the second module) on a third signal path coupled to the master device. In a second mode of operation, the first memory module provides first read data from its plurality of integrated circuit memory devices (via the integrated circuit buffer device) on the first signal path and second read data from its plurality of integrated circuit memory devices (via the integrated circuit buffer device) on a second signal path that is coupled to a second memory module. An integrated circuit buffer device in the second memory module then bypasses the second read data from the second signal path and provides the second read data on a third signal path coupled to the master device. The first memory module may have a larger address space or capacity, such as twice as large, as compared to the second memory module.

Similarly, write data may be provided from the master device to the first and second memory modules during the first and second modes of operation.

According to embodiments, the second memory module includes a bypass circuit (such as in the integrated circuit buffer device, interface or in continuity memory module) to transfer the second read data from the second signal path to the third signal path. The bypass circuit may include a jumper, signal trace and/or semiconductor device. The bypass circuit may also include delay circuits for adding delay in outputting the read data (or levelizing) from a memory module.

According to embodiments, a system includes a master device and at least four memory modules wherein at least two memory modules have different capacities than the other two memory modules. The four memory modules are coupled to a plurality of signal paths. The system may operate in a bypass mode in which one or more memory modules use a bypass circuit to provide read data from at least one larger capacity memory module to a master device.

According to embodiments, a system includes a master and a plurality of memory modules that may be disposed in a variety of topologies, such as point-to-point or daisy chain topologies. Memory modules may include a plurality of integrated circuit buffer devices that are coupled using a variety of topologies to receive control information, such as dedicated, fly-by, stub, serpentine or tree topologies, singly or in combination.

According to embodiments, a method determines a mode of operation of a system including a master and a plurality of memory modules. In a bypass mode of operation, delays are provided to read data from at least one memory module to levelize or ensure that read data from different capacity memory modules using different signal paths arrive at the master at approximately the same time.

According to embodiments, a memory module includes a plurality of signal paths that provide data to a memory module connector from a plurality of respective integrated circuit buffer devices (or dies) that access the data from an associated plurality of integrated circuit memory devices (or dies). In a specific embodiment, each integrated circuit buffer device is also coupled to a bussed signal path that provides control and/or address information that specifies an access to at least one integrated circuit memory device associated with the respective integrated circuit buffer device.

According to embodiments, a memory module connector includes a control/address interface portion and a data interface portion. A control/address bus couples a plurality of integrated circuit buffer devices to the control/address interface portion. A plurality of data signal paths couple the plurality of respective integrated circuit buffer devices to the data interface portion. Each integrated circuit buffer device includes 1) an interface to couple to at least one integrated circuit memory device, 2) an interface to couple to the control/address bus and 3) an interface to couple to a data signal path in the plurality of data signal paths.

According to embodiments, a memory module may include a non-volatile memory location, for example using an electrically erasable programmable read only memory (“EEPROM”) (also known as a Serial Presence Detect (“SPD”) device), to store information regarding parameters and configuration of the memory module. In embodiments, at least one integrated circuit buffer device accesses information stored in the SPD device.

In a package embodiment, a package houses an integrated circuit buffer die and the plurality of integrated circuit memory dies. In the package, a plurality of signal paths transfer data (read and/or write data) between the integrated circuit buffer die and the plurality of integrated circuit memory dies. The integrated circuit buffer die provides control signals from an interface of the package to the plurality of integrated circuit memory dies. Data stored in memory arrays of the plurality of integrated circuit memory dies is provided to a signal path disposed on the memory module via the integrated circuit buffer die in response to the control signals. In an embodiment, the package may be a multichip package (“MCP”). In an embodiment, the plurality of integrated circuit memory dies may be housed in common or separate packages. In an embodiment described below, the memory module may include a series of integrated circuit dies (i.e., memory die and buffer die) stacked on top of one another and coupled via a signal path.

As described herein, an integrated circuit buffer device is also referred to as a buffer or buffer device. Likewise, an integrated circuit memory device is also referred to as a memory device. A master device is also referred to as a master.

In an embodiment, an integrated circuit memory device is distinguished from a memory die in that a memory die is a monolithic integrated circuit formed from semiconductor materials for storing and/or retrieving data or other memory functions, whereas an integrated circuit memory device is a memory die having at least some form of packaging or interface that allows the memory die to be accessed.

Likewise in an embodiment, an integrated circuit buffer device is distinguished from a buffer die in that a buffer die is a monolithic integrated circuit formed from semiconductor materials and performs at least one or more buffer functions described herein, whereas an integrated circuit buffer device is a buffer die having at least some form of packaging or interface that allows communication with the buffer die.

In the embodiments described in more detail below, FIGS. 1-8 illustrate control/address and data signal path topologies including a plurality of integrated circuit memory devices (or dies) and a plurality of integrated circuit buffer devices (or dies) situated on a memory module. FIGS. 10, 18, and 19 also illustrate signal path topologies including integrated circuit memory devices (or dies) and integrated circuit buffer devices (or dies) situated on a memory module as well as the operation of an integrated circuit buffer device (or die) and memory device (or die) in embodiments among other things. FIGS. 21A-D, 22A-C, 23A-C and 24A-B illustrate system topologies. FIGS. 26A-B, 28A-B and 31 illustrate operating a memory system in a first and second mode of operation (bypass mode).

FIG. 1 illustrates a memory module topology including a plurality of integrated circuit memory devices and a plurality of associated integrated circuit buffer devices. In an embodiment, a memory module 100 includes a plurality of buffer devices 100 a-d coupled to a common address/control signal path 121. Each buffer device of the plurality of buffer devices 100 a-d provides access to a plurality of respective integrated circuit memory devices 101 a-d via signal paths 102 a-d and 103. In an embodiment, respective data slices a-d are formed by one of buffers 100 a-d and sets of memory devices 101 a-d. Buffer devices 100 a-d are coupled to signal paths 120 a-d, respectively, that transfer data (read and write data) between the buffer devices 100 a-d and a memory module connector interface. In an embodiment, mask information is transferred to buffer devices 100 a-d from a memory module connector interface using signal paths 120 a-d, respectively.

In an embodiment, a data slice is a portion of the memory module data signal path (or bus) that is coupled to the respective integrated circuit buffer device. The data slice may include the full data path or portions of data paths to and from a single memory device disposed on the memory module.

Integrated circuit memory devices may be considered as a common class of integrated circuit devices that have a plurality of storage cells, collectively referred to as a memory array. A memory device stores data (which may be retrieved) associated with a particular address provided, for example, as part of a write or read command. Examples of types of memory devices include dynamic random access memory (“DRAM”), including single and double data rate synchronous DRAM, static random access memory (“SRAM”), and flash memory. A memory device typically includes request or command decode and array access logic that, among other functions, decodes request and address information, and controls memory transfers between a memory array and signal path. A memory device may include a transmitter circuit to output data, for example, synchronously with respect to rising and falling edges of a clock signal, (e.g., in a double data rate type of memory device). Similarly, the memory device may include a receiver circuit to receive data, for example, synchronously with respect to rising and falling edges of a clock signal or outputs data with a temporal relationship to a clock signal in an embodiment. A receiver circuit also may be included to receive control information synchronously with respect to rising and falling edges of a clock signal. In an embodiment, strobe signals may accompany the data propagating to or from a memory device and that data may be captured by a device (e.g., memory device or buffer, or controller) using the strobe signal.

In an embodiment, an integrated circuit buffer device is an integrated circuit that acts as an interface between a memory module connector interface and at least one integrated circuit memory device. In embodiments, the buffer device may store and/or route data, control information, address information and/or a clock signal to at least one integrated circuit memory device that may be housed in a common or separate package. In an embodiment, the buffer isolates, routes and/or translates data, control information and a clock signal, singly or in combination, between a plurality of memory devices and a memory module connector interface. An embodiment of a memory module connector interface is described below and shown in FIGS. 9A-C.

At least one signal path 121, as shown in FIG. 1, disposed on memory module 100, transfers control and/or address (control/address) information between at least one of the buffer devices 100 a-d and a memory module connector interface in various embodiments. In an embodiment, signal path 121 is a multi-drop bus. As illustrated in FIGS. 2-8 and described below, alternate topologies for transferring control/address information, data and clock signals between one or more buffer devices 100 a-d and a memory module connector interface may be used in alternate embodiments. For example, a split multi-drop control/address bus, segmented multi-drop control/address bus, and point-to-point and/or daisy chain topologies for a data bus may be employed.

In an embodiment, clock signals and/or clock information may be transferred on at least one signal line in signal path 121. These clock signal(s) provide one or more clock signals having a known frequency and/or phase. In an embodiment, a clock signal is synchronized with or travels along side the control/address information. In an embodiment, an edge of the clock signal has a temporal relationship with an edge of a control/address signal representing the control/address information. In an embodiment, a clock signal is generated by a clock source, master device (e.g., controller device) and/or buffer device.

In an embodiment, a clock signal and/or clock information may be transferred on at least one signal line in respective signal paths 120 a-d. Buffer devices 100 a-d may receive and/or transmit a clock signal with data on signal paths 120 a-b. In an embodiment, write data is provided to buffer devices 100 a-d on signal paths 120 a-d and a clock signal is provided on signal paths 120 a-d along side write data. In an embodiment, a clock signal (such as a clock-to-master (“C™”)) is provided from buffer devices 100 a-d on signal paths 120 a-d along side read data on signal paths 120 a-d. In an embodiment, a clock signal is synchronized with or travels along side the write and/or read data. An edge of the clock signal has a temporal relationship or is aligned with an edge of a data signal representing write and/or read data. Clock information can be embedded in data, eliminating the use of separate clock signals along with the data signals.

In an embodiment, a read, write and/or bidirectional strobe signal may be transferred on at least one signal line in respective signal paths 120 a-d. Buffer devices 100 a-d may receive and/or transmit a strobe signal with data on signal paths 120 a-b. In an embodiment, write data is provided to buffer devices 100 a-d on signal paths 120 a-d and a strobe signal is provided on signal paths 120 a-d along side write data. In an embodiment, a strobe signal is provided from buffer devices 100 a-d on signal paths 120 a-d along side read data on signal paths 120 a-d. In an embodiment, a strobe signal is synchronized with or travels along side the write and/or read data. An edge of the strobe signal has a temporal relationship or is aligned with an edge of a data signal representing write and/or read data.

In an embodiment, addresses (for example, row and/or column addresses) for accessing particular memory locations in a particular integrated circuit memory device and/or commands are provided on signal path 121 from a memory module connector interface. In an embodiment, a command relates to a memory operation of a particular integrated circuit memory device. For example, a command may include a write command to store write data at a particular memory location in a particular integrated circuit memory device and/or a read command for retrieving read data stored at a particular memory location from a particular integrated circuit memory device. Also, multiple memory devices in different data slices can be accessed simultaneously. In embodiments, a command may include row commands, column commands such as read or write, mask information, precharge and/or sense command. In an embodiment, control information is transferred on signal path 121 over a common set of lines in the form of a time multiplexed packet where particular fields in the packet are used for including command operation codes and/or addresses. Likewise, packets of read data may be transferred from integrated circuit memory devices via buffers 100 a-d on respective signal paths 120 a-d to a memory module connector interface. In an embodiment, a packet represents one or more signals asserted at particular bit windows (or a time interval) for asserting a signal on particular signal lines.

In embodiments, memory module 100 communicates (via a memory module connector interface) with a master device (e.g., a processor or controller).

FIG. 2 illustrates an embodiment of a memory module topology having a split multi-drop control/address/clock bus. In particular, memory module 200 includes a split multi-drop control/address bus 221 coupled to buffers 100 a-d and a memory module connector interface. With reference to FIG. 2, a first portion of bus 221 is terminated by termination 230 and a second portion of bus 221 is terminated by termination 231. In an embodiment, the impedance of termination 230 matches the impedance of the first portion of bus 221 (Z0) coupled to buffers 100 c-d and the impedance of termination 231 matches the impedance of the second portion of bus 221 (Z1) coupled to buffers 100 a-b. In an embodiment, impedance Z0 equals impedance Z1. In embodiments, terminations 230 and 231, singly or in combination, are disposed on memory module 100, buffer devices 100 a and 100 d or packages used to house buffer devices 100 a and 100 d.

FIG. 3 illustrates a memory module topology having a single multi-drop control/address/clock bus terminated by termination 330. In an embodiment, the impedance of termination 330 matches the impedance of signal path 121 (or control/address/clock bus). In embodiments, termination 330, singly or in combination, is disposed on memory module 300 or on buffer device 100 d.

FIG. 4 illustrates a memory module topology that provides data between each integrated circuit buffer device and a memory module connector interface. In an embodiment, each signal path 120 a-d is terminated by an associated termination 420 a-d, respectively. In an embodiment, terminations 420 a-d have respective impedances that match the impedance Z0 of each of the signal paths 120 a-d. In embodiments, terminations 420 a-d, singly or in combination, are disposed on memory module 400, each of buffer devices 100 a-d or packages used to house buffer devices 100 a-d.

Referring to FIG. 1, a control/address signal rate ratio of signal path 121 to signal path 103 may be 2:1 (or other multiples such as 4:1, 8:1, etc.) so that a memory module connector interface is able to operate as fast as specified while memory devices 101 a-d may operate at half (quarter, eighth, etc) the control/address signaling rate so that relatively lower cost memory devices may be used. Similarly, a data signal rate of one of signal paths 102 a-d to one of signal paths 120 a-d may be 2:1 (or other multiple such as 4:1, 8:1, etc) so that a memory module connector interface is able to operate as fast as specified while memory devices 101 a-d may operate at half (quarter, eighth, etc.) the data signaling rate so that relatively lower cost memory devices may be used.

FIG. 5 illustrates a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices with an integrated circuit buffer device 501 for control, address and/or clock information. Memory module 500 is similar to memory module 100 except that buffer device 501 is coupled to signal paths 121 and 121 a-b. Buffer device 501 outputs control, address and/or clock information to buffer devices 100 a-b on signal path 121 a and to buffer devices 100 c-d on signal path 121 b. In an embodiment buffer device 501 copies control, address and/or clock information received on signal path 121 and repeats the control, address and/or clock information on signal paths 121 a-b. In an embodiment, buffer device 501 is a clocked buffer device that provides a temporal relationship with control and address information provided on signal paths 121 a-b. In an embodiment, signal paths 121 a-b include at least one signal line to provide a clock signal and/or clock information. In an embodiment, buffer device 501 includes a clock circuit 1870 as shown in FIG. 18. In an embodiment, buffer device 501 receives control information, such as a packet request, that specifies an access to at least one of the integrated circuit memory devices 101 a-d and outputs a corresponding control signal (on signal path 121 a and/or 121 b) to the specified integrated circuit memory device.

FIG. 6 illustrates a memory module topology similar to that illustrated in FIG. 5 except that a termination 601 is coupled to signal path 121 on memory module 600. In an embodiment, the impedance of termination 601 matches the impedance Z0 of signal path 121. In embodiments, termination 601 is disposed on memory module 600, buffer device 501 or a package used to house buffer device 501.

FIG. 7 illustrates a memory module topology that provides data to and/or from each integrated circuit buffer device and terminations coupled to signal paths. In an embodiment, each signal path 120 a-d is terminated by associated terminations 701 a-d, respectively. In an embodiment, terminations 701 a-d have respective impedances that match the impedance Z0 of each of the signal paths 120 a-d. In embodiments, terminations 701 a-d, singly or in combination, are disposed on memory module 700, buffer devices 100 a-d or packages used to house buffer devices 100 a-d.

FIG. 8 illustrates a memory module topology having a split multi-drop signal path between a buffer device for control, address and/or clock information and the plurality of buffer devices. In particular, memory module 800 includes a split multi-drop control/address bus 121 a-b coupled to buffers 100 a-d and a buffer device 501. In an embodiment, a first portion of bus 121 a is terminated by termination 801 and a second portion of bus 121 b is terminated by termination In an embodiment, the impedance of termination 801 matches the impedance of the first leg (Z0) and the impedance of termination 802 matches the impedance of the second leg (Z1). In an embodiment, impedance Z0 equals impedance Z1. In embodiments, terminations 801 and 802, singly or in combination, are disposed on memory module 800, buffer devices 100 a and 100 d or packages used to house buffer devices 100 a and 100 d.

Referring to FIG. 5, a control/address signal rate ratio of signal path 121 to signal path 121 a (or 121 b) to signal path 103 may be 2:1:1 (or other multiples such as 4:1:1, 8:1:1, etc.) so that other multi-drop bus topology embodiments using signal paths 121 a (or 121 b) and signal path 103 do not have to necessarily operate as high a signal rate as an embodiment that uses signal path 121 as shown in FIG. 1. Also like FIG. 1, a control/address signal rate ratio of signal path 121 to signal path 103 may be 2:1 (or other multiples such as 4:1, 8:1, etc.) so that a memory module connector interface is able to operate as fast as specified while memory devices 101 a-d may operate at half (or quarter, eighth, etc.) the control/address signaling rate so that relatively lower cost memory devices may be used. Similarly, a data signal rate of one of signal paths 102 a-d to one of signal paths 120 a-d may be 2:1 (or other multiple such as 4:1, 8:1, etc.) so that a memory module connector interface is able to operate as fast as the specified signaling rate while memory devices 101 a-d may operate at half (or quarter, eighth, etc.) the data signaling rate so that relatively lower cost memory devices may be used.

FIG. 9A illustrates a top view of a memory module topology including a plurality of integrated circuit memory devices and a plurality of integrated circuit buffer devices coupled to a connector interface. In an embodiment, memory module 900 includes a substrate 910 having a standard dual in-line memory module (“DIMM”) form factor or other module form factor standards, such as small outline DIMM (“SO-DIMM”) and very low profile DIMM (“VLP-DIMM”). In alternate embodiments, substrate 910 may be, but is not limited to, a wafer, printed circuit board (“PCB”), package substrate like BT epoxy, flex, motherboard, daughterboard or backplane, singly or in combination.

In an embodiment, memory module 900 includes pairs of memory devices 101 a-b and buffer devices 100 a-d disposed on a first side of substrate 910. In alternate embodiments, more or less memory devices and buffer devices are used. In an embodiment, pairs of memory devices 101 c-d are also disposed on a second side of memory module 900 as shown in a side and bottom view of memory module 900 in FIGS. 9B and 9C. In an embodiment, each memory device and buffer device are housed in separate packages. In alternate embodiments, memory devices and buffer devices may be housed in MCP package embodiments described herein.

Memory module 900 includes connector interface 920 that has different interface portions for transferring data and control/address/clock signals. For example, a first side of memory module 900 includes connector interface portions 920 a-d used to transfer data signals and a connector interface portion 930 a used to transfer control/address signals. In an embodiment, connector interface portion 930 a also transfers a clock signal and/or clock information. In an embodiment, a second side of memory module 900 including connector interface portions 920 e-h are used to transfer data signals and a connector interface portion 930 b is used to transfer control/address signals. In an embodiment, connector interface portion 930 b also transfers a clock signal and/or clock information.

In an embodiment, connector interface 920 is disposed on an edge of substrate 910. In an embodiment, a memory module 900 is inserted into a socket 940 disposed on substrate 950. In an embodiment, substrate 950 is a main board or PCB with signal paths 960 a-b for transferring signals on substrate 950. In an embodiment, signal paths 960 a and 960 b are signal traces or wires. In an embodiment, signal paths 960 a and 960 b are coupled to other sockets disposed on substrate 950 that may have another memory module inserted and/or coupled to a master.

In an embodiment, connector interface portions include at least one contact or conducting element, such as a metal surface, for inputting and/or outputting an electrical signal. In alternate embodiments, a contact may be in the form of a ball, socket, surface, signal trace, wire, a positively or negatively doped semiconductor region and/or pin, singly or in combination. In an embodiment, a connector interface as described herein, such as connector interface 920, is not limited to physically separable interfaces where a male connector or interface engages a female connector (or socket 940) or interface. A connector interface also includes any type of physical interface or connection, such as an interface used in a system-in-a-package (“SIP”) where leads, solder balls or connections from a memory module are soldered to a circuit board.

In an alternate embodiment, memory module 900 is included in an embedded memory subsystem, such as one in a computer graphics card, video game console or a printer. In an alternate embodiment, memory module 900 is situated in a personal computer or server.

In an embodiment, a master communicates with memory modules illustrated in FIGS. 1-9 and 16-17. A master may transmit and/or receive signals to and from the memory modules illustrated in FIGS. 1-9 and 16-17. A master may be a memory controller, peer device or slave device. In embodiments, a master is a memory controller, which may be an integrated circuit device that contains other interfaces or functionality, for example, a Northbridge chip of a chipset. A master may be integrated on a microprocessor or a graphics processor unit (“GPU”) or visual processor unit (“VPU”). A master may be implemented as a field programmable gate array (“FPGA”). Memory modules, signal paths, and a master may be included in various systems or subsystems such as personal computers, graphics cards, set-top boxes, cable modems, cell phones, game consoles, digital television sets (for example, high definition television (“HDTV”)), fax machines, cable modems, digital versatile disc (“DVD”) players or network routers.

In an embodiment, a master, memory modules and signal paths are in one or more integrated monolithic circuits disposed in a common package or separate packages.

FIG. 10 is a block diagram illustrating an embodiment of a device 1000 having a plurality of integrated circuit memory devices 101 a-d and a buffer 100 a. Here, data (read and/or write) may be transferred between the plurality of integrated circuit memory devices 101 a-d and buffer 100 a on a signal path 1006 (data). Signal path 1006 is a signal path situated internal to device 1000 and corresponds to signal paths 1113 a-d and 1114 shown in FIG. 11. Signal path 1006 is a bus for providing bidirectional data signals between a plurality of integrated circuit memory devices 101 a-d and buffer 100 a. An example of bidirectional data signals includes signals traveling from one or more of integrated circuit memory devices 101 a-d to buffer 100 a and also signals traveling from buffer 100 a to one or more of integrated circuit memory devices 101 a-d. Signal path 1005 is a signal path internal to device 1000 and corresponds to signal paths 1116 a-d and 1117 shown in FIG. 11. Signal path 1005 is a bus for providing unidirectional control/address/clock signals from a buffer 100 a to a plurality of integrated circuit memory devices 101 a-d. In an example of a unidirectional bus, signals travel in only one direction, i.e., in this case, from only buffer 100 a to one or more of integrated circuit memory devices 101 a-d. Signal path 1005 includes individual control signal lines, for example, a row address strobe line, column address strobe line, etc., and address signal lines. Signal path 1005 may include a fly-by clock line to transfer a clock signal from buffer 100 a to integrated circuit memory devices 101 a-d. Signal path 1005 may transfer a clock signal from one or more integrated circuit memory devices 101 a-d to buffer 100 a.

In an embodiment, buffer 100 a communicates with a serial presence detect (“SPD”) device to store and retrieve parameters and configuration information regarding device 1000 and/or memory module 900. In an embodiment, an SPD 1002 is a non-volatile storage device. Signal path 1004 couples SPD 1002 to buffer 100 a. In an embodiment, signal path 1004 is an internal signal path for providing bidirectional signals between SPD 1002 and buffer 100 a.

In an embodiment, SPD 1002 is an EEPROM device. However, other types of SPD 1002 are possible, including but not limited to a manual jumper or switch settings, such as pull-up or pull-down resistor networks tied to a particular logic level (high or low), which may change state when a memory module is added or removed from a system.

In an embodiment, SPD 1002 is a memory device that includes registers that stores configuration information that can be easily changed via software during system operation, allowing a high degree of flexibility, and making configuration operations that are transparent to an end user.

In an embodiment illustrated in FIG. 18, functionality of the SPD mentioned above may be integrated into buffer device 100 a using a register set, such as configuration register set 1881. Referring to FIG. 18, SPD logic and interface 1820 c may be preconfigured with information pertaining to the buffer and memory devices connected to the buffer, or may store information pertaining to only one of the memory devices or the buffer device 100 a. Control inputs to the buffer may determine when a storage node within the register set will sample the information to preload or preconfigure the SPD logic and interface 1820 c. The term register may apply either to a single-bit-wide register or multi-bit-wide register.

In an embodiment illustrated by FIG. 10, SPD 1002 stores information relating to configuration information of memory module 900 or a memory system. For example, configuration information may include repair and redundancy information to repair a defective memory device, defective memory cells or peripheral circuits on a memory device, and/or signal path. In an embodiment, SPD configuration information includes memory module population topology, such as a number, a position and a type of memory device in a package and/or on a memory module, or rank, if any. SPD configuration information may include an amount of memory capacity of one or more memory modules and/or timing information to levelize signals between memory modules and a master device in a memory system. In an embodiment, SPD configuration information includes a serialization ratio for interfaces in a buffer and/or information regarding configuring the width of a buffer. In an embodiment, SPD configuration information includes a first value that represents the desired width of buffer device 100 a or includes multiple values that represent the range of possible widths of the buffer device 100 a, and a second value that represents the desired width of interface 1820 b as illustrated in FIG. 18.

In an embodiment, SPD configuration information includes timing information or parameters for accessing memory devices, such as a time to access a row or the memory device, a time to access a column of the memory device, a time between a row access and a column access, a time between a row access and a precharge operation, a time between a row sense applied to a first bank of a memory array and a row sense applied to a second bank of the memory array and/or a time between a precharge operation applied to a first bank in a memory array and a precharge operation applied to a second bank of the memory array.

In an embodiment, the stored timing information may be expressed in terms of time units where a table of values maps specific time units to specific binary codes. During an initialization or calibration sequence, a master or a buffer may read SPD configuration information and determine the proper timing information for one or more memory devices. For example, a master may also read information representing the clock frequency of a clock signal from an SPD 1002, and divide the retrieved timing information by a clock period of a clock signal. (The clock period of the clock signal is the reciprocal of the clock frequency of the clock signal). Any remainder resulting from this division may be rounded up to the next whole number of clock cycles of the clock signal.

Signal paths 120 a and 121, as shown in FIG. 10, are coupled to buffer 100 a. In an embodiment, signal path 120 a transfers unidirectional control/address/clock signals to buffer 100 a. In an embodiment, signal path 121 transfers bidirectional or unidirectional data signals to and from buffer 100 a. Other interconnect and external connect topologies may also be used for device 1000 in alternate embodiments. For example, buffer 100 a may be coupled to a single multi-drop control bus, a split multi-drop control bus, or a segmented multi-drop bus.

In an embodiment, device 1000 has two separate power sources. Power source V1 supplies power to one or more memory devices (memory devices 101 a-d) on memory module 900. Power source V2 supplies power to one or more buffers (buffer 100 a) on memory module 900. In an embodiment, the buffer 100 a has internal power regulation circuits to supply power to the memory devices 101 a-d.

FIG. 11 illustrates a device 1100 including a plurality of integrated circuit memory dies 1101 a-d and a buffer die 1100 a housed in or upon a common package 1110 according to embodiments. As described herein in other embodiments and illustrated in FIGS. 12-15, a plurality of integrated circuit memory dies 1101 a-d and buffer 1100 a are disposed in multiple package type embodiments. For example, a plurality of integrated circuit memory dies 1101 a-d and a buffer die 1100 a may be stacked, on a flexible tape, side-by-side or positioned in separate packages on a device substrate. Buffer die 1100 a is used to provide signals, including control/address/clock information and data, between a plurality of integrated circuit memory dies 1101 a-d and a device interface 1111 that includes contacts 1104 a-f. In an embodiment, one or more contacts 1104 a-f is similar to contacts of connector interface 920. Contacts 1104 a-f are used to couple device 1100 to substrate 910, and in particular to signal paths 120 a and 121, of memory module 100 in an embodiment. Device interface 1111 also includes signal paths 1118 and 1115 to transfer signals between contacts 1104 a-f and buffer 100 a via buffer interface 1103. Signals are then transferred between a plurality of memory dies 1101 a-d and buffer die 1100 a via buffer interface 1103 and signal paths 1117 (disposed in device interface 1111) and 1116 a-d as well as signal paths 1114 (disposed in device interface 1111) and 1113 a-d. In an embodiment, spacers 1102 a-c are positioned between integrated circuit memory dies 1101 a-d. In an embodiment, spacers 1102 a-c are positioned to dissipate heat. Similarly, buffer die 1100 a is disposed away from a plurality of integrated circuit memory dies 1101 a-d to alleviate heat dissipation near the memory devices. In an embodiment, signal paths are coupled to each other and integrated circuit memory dies 1101 a-d by a solder ball or solder structure.

FIG. 12 illustrates a stacked package device 1200 having a package 1210 containing a plurality of integrated circuit memory dies 1101 a-d and a separate package 1290 having a buffer die 1100 a. Both packages 1210 and 1290 are stacked and housed to make device 1200. In an embodiment, a plurality of integrated circuit memory dies has separate packages and is stacked on package 1290. Device 1200 has similar components illustrated in FIG. 11. Buffer die 1100 a communicates with a plurality of integrated circuit memory dies 1101 a-d as described herein. Device 1200 has memory dies 1101 a-d stacked upon buffer die 1100 a and separated by contacts 1201 a-d. In an embodiment, contacts 1201 a-d are solder balls that couple signal paths 1117 and 1114 to signal paths 1202 and 1203 that are coupled to buffer interface 1103.

FIG. 13 illustrates devices 1300 and 1301 having a plurality of integrated circuit memory devices 101 a-b (101 a-c in device 1301) and a buffer device 100 a that are disposed on a flexible tape 1302 according to embodiments. Buffer device 100 a communicates with a plurality of integrated circuit memory devices as described herein. Signal path 1305 disposed on or in flexible tape 1302 transfers signals between a plurality of integrated circuit memory devices 101 a-c and buffer 100 a. Contacts, such as a grid array of balls 1304, couple each integrated circuit memory device in a plurality of integrated circuit memory devices 101 a-c and a buffer 100 a to signal path 1305 in flexible tape 1302 in an embodiment. Adhesive 1303 may be used to couple a plurality of integrated circuit memory devices 101 a-c to each other and to a buffer 100 a in an embodiment. Device 1300 and 1301 are disposed in common package in an embodiment.

FIG. 14 illustrates a device 1400 having a plurality of integrated circuit memory dies 1101 a-d and 1401 a-d and a buffer die 1100 a that are disposed side-by-side and housed in a package 1410. Device 1400 has similar components illustrated in FIG. 11. Buffer die 1100 a communicates with a plurality of integrated circuit memory dies 1101 a-d and 1401 a-d as described herein. In an embodiment, a plurality of integrated circuit memory dies 1101 a-d and 1401 a-d and a buffer die 1100 a are disposed side-by-side on a substrate 1450 that is coupled to device interface 1411. A plurality of integrated circuit memory dies 1401 a-d is separated by spacers 1402 a-c. In an embodiment, a single integrated circuit memory die 1101 d and a single integrated circuit memory die 1401 d are disposed side-by-side with buffer die 1100 a. Device interface 1411 includes contacts 1104 a-f. Signals are transferred between buffer interface 1103 and contacts 1104 a-f by signal paths 1418 and 1415. Signals are transferred between buffer interface 1103 and signal paths 1116 a-d (or integrated circuit memory dies 1101 a-d) by signal path 1417. Similarly, signals are transferred between buffer interface 1103 and signal paths 1113 a-d (or integrated circuit memory dies 1401 a-d) by signal path 1414.

FIG. 15 illustrates a device 1500 having a plurality of integrated circuit memory dies 1101 a-b and a buffer die 1100 a that are housed in separate packages 1501, 1505 and 1520, respectively. Device 1500 has similar components illustrated in FIG. 11. Buffer die 1100 a communicates with integrated circuit memory dies 1101 a-b as described herein. Integrated circuit memory dies 1101 a-b and a buffer die 1100 a are disposed on substrate 1530 that includes signal paths 1504, 1509, 1515 and 1518. Integrated circuit memory die 1101 a includes memory interface 1507 having contacts 1508. Integrated circuit memory die 1101 b includes memory interface 1503 having contacts 1541. Buffer die 1100 a includes a buffer interface 1103 having contacts 1560. Signals are transferred between buffer interface 1103 and contacts 1104 a-f by signal paths 1515 and 1518. Signals are transferred between buffer interface 1103 and integrated circuit memory die 1101 a by signal path 1509 via memory interface 1507 and contacts 1508. Similarly, signals are transferred between buffer interface 1103 and integrated circuit memory die 1101 b by signal path 1504 via memory interface 1503 and contacts 1541. As described herein, device 1500 is coupled to a memory module 900 via contacts 1104 a-f.

FIG. 16 illustrates a memory module having an SPD 1603 according to an embodiment. Memory module 1610 includes a plurality of integrated circuit memory devices (or dies) and buffer devices (or dies) disposed on substrate 930 along with SPD 1603. FIG. 16 illustrates a memory module 1610 having a single SPD 1603 that can be accessed by each buffer device 100 a-b positioned on substrate 930. Signal path 1601 allows access to SPD 1603 from connector interface 920 and one or more buffers 100 a-b. In an embodiment, signal path 1601 is a bus. SPD 1603 may have configuration and/or parameter information written to or read by a master by way of connector interface 920 and signal path 1601. Likewise, buffers 100 a-b may write to or read from SPD 1603 via signal path 1601.

FIG. 17 illustrates a memory module 1710 with each device 1711 a-b or data slice a-b having an associated SPD 1720 a-b, buffer device (or die) 100 a-b and at least one integrated circuit memory device 101 a (or die) according to an embodiment. The plurality of buffers 100 a-b and associated plurality of SPDs 1720 a-b are disposed on substrate 930. Configuration and/or parameter information is accessed from SPDs 1720 a-b using signal path 1701, which is coupled, to connector interface 920 and each SPD 1720 a-b. In particular, signal path 1701 couples SPD 1720 a-b of device 1711 a-b to connector interface 920. In an embodiment, signal path 1701 is a bus. In an alternate embodiment, signal path 1701 couples SPD 1720 a and SPD 1720 b in a daisy chain or serial topology. In an embodiment, one or more buffer devices 100 a-b of devices 1711 a-b may access (read and/or write) respective SPDs 1720 a-b. Likewise, a master may access (read and/or write) respective SPDs 1720 a-b using signal path 1701. In an embodiment, configuration and/or parameter information is transferred using a header field or other identifier so that SPDs coupled in a daisy chain may forward the SPD information to the intended destination SPD.

FIG. 18 illustrates a block diagram of a buffer device 100 a (or die, such as buffer die 1100 a) according to embodiments. Buffer 100 a includes buffer interface 1103 a, interfaces 1820 a-c, redundancy and repair circuit 1883, multiplexer 1830, request and address logic circuit 1840, data cache and tags circuit 1860, computations circuit 1865, configuration register set 1881, and clock circuit 1870, singly or in combination.

In a memory read operation embodiment, buffer 100 a receives control information (including address information) that may be in a packet format from a master on signal path 121 and in response, transmits corresponding signals to one or more, or all of memory devices 101 a-d on one or more signal paths 1005. One or more of memory devices 101 a-d may respond by transmitting data to buffer 100 a which receives the data via one or more signal paths 1006 and in response, transmits corresponding signals to a master (or other buffer). A master transmits the control information via one or more signal paths 121 and receives the data via one or more signal paths 120 a.

By bundling control and address information in packets, protocols required to communicate to memory devices 101 a-d are independent of the physical control/address interface implementation.

In a memory write operation embodiment, buffer 100 a receives control information (including address information) that may be in a packet format from a master on signal path 121 and receives the write data for one or more memory devices 101 a-d that may be in a packet format from a master on signal path 120 a. Buffer 100 a then transmits corresponding signals to one or more, or all of memory devices 101 a-d on one or more signal paths 1006 so that the write data may be stored.

A master transmits the control/address/clock information via one or more signal paths 121 and transmits the write data via one or more signal paths 120 a.

In an embodiment, simultaneous write and/or read operations may occur for different memory devices in memory devices 101 a-d.

In an embodiment, control information that is provided to buffer 100 a causes one or more memory operations (such as write and/or read operations) of one or more memory devices 100 a-d, while the same control information may be provided to buffer 100 b which causes the same memory operations of one or more memory devices 100 a-d associated with buffer 100 b. In another embodiment, the same control information may be provided to buffer 100 a and buffer 100 b, yet different memory operations occur for the one or more memory devices 100 a-d associated with each buffer 100 a-b.

In an embodiment, buffer interface 1103 a couples signal paths 121 and 120 a to buffer 100 a as shown in FIG. 10. In an embodiment, buffer interface 1103 a corresponds to buffer interface 1103 shown in FIGS. 11, 12, 14 and 15. In an embodiment, buffer interface 1103 a includes at least one transceiver 1875 (i.e. transmit and receive circuit) coupled to signal path 120 a to transmit and receive data and at least one receiver circuit 1892 coupled to signal path 121 to receive control/address/clock information. In an embodiment, signal paths 121 and 120 a include point-to-point links. Buffer interface 1103 a includes a port having at least one transceiver 1875 that connects to a point-to-point link. In an embodiment, a point-to-point link comprises one or a plurality of signal lines, each signal line having no more than two transceiver connection points. One of the two transceiver connection points is included on buffer interface 1103 a. Buffer interface 1103 a may include additional ports to couple additional point-to-point links between buffer 100 a and other buffer devices on other devices and/or memory modules. These additional ports may be employed to expand memory capacity as is described in more detail below. Buffer 100 a may function as a transceiver between a point-to-point link and other point-to-point links. In an embodiment, buffer interface 1103 a includes a repeater circuit 1899 to repeat data, control information and/or a clock signal. In an embodiment, buffer interface 1103 a includes a bypass circuit 1898 to transfer signals between connector interface portions.

In an embodiment, termination 1880 is disposed on buffer 100 a and is connected to transceiver 1875 and signal path 120 a. In this embodiment, transceiver 1875 includes an output driver and a receiver. Termination 1880 may dissipate signal energy reflected (i.e., a voltage reflection) from transceiver 1875. Termination 1880, as well as other termination described herein, may be a resistor or capacitor or inductor, singly or a series/parallel combination thereof. In alternate embodiments, termination 1880 may be external to buffer 100 a. For example, termination 1880 may be disposed on a substrate 910 of a memory module 900 or on a package used to house buffer 100 a.

Interface 1820 a includes at least one transmitter circuit 1893 coupled to signal path 1005 to transmit control/address/clock information to one or more memory devices. In an embodiment, interface 1820 a includes a transceiver that may transfer control/address/clock information between buffers disposed on a common memory module or different memory modules.

Interface 1820 b includes a transceiver 1894 coupled to signal path 1006 to transfer data between buffer 100 a and one or more memory devices 101 a-d as illustrated in FIG. 10. SPD logic and interface 1820 c includes a transceiver 1896 coupled to signal path 1004 to transfer configuration and/or parameter information between buffer 100 a and an SPD 1002 as illustrated in FIG. 10. In an embodiment, interface 1820 c is used to transfer configuration and/or parameter information as illustrated in FIGS. 16 and 17.

According to an embodiment, multiplexer 1830 may perform bandwidth-concentrating operations between buffer interface 100 a and interface 1820 b as well as route data from an appropriate source (i.e. target a subset of data from memory devices, internal data, cache or write buffer). The concept of bandwidth concentration involves combining the (smaller) bandwidth of each data path coupled to a memory device in a multiple data signal path embodiment to match the (higher) overall bandwidth utilized by buffer interface 1103 a. In an embodiment, multiplexing and demultiplexing of throughput between the multiple signal paths that may be coupled to interface 1820 b and buffer interface 1103 a is used. In an embodiment, buffer 101 a utilizes the combined bandwidth of multiple data paths coupled to interface 1820 b to match the bandwidth of interface buffer interface 1103 a.

In an embodiment, data cache and tags circuit 1860 (or cache 1860) may improve memory access time by providing storage of most frequently referenced data and associated tag addresses with lower access latency characteristics than those of the plurality of memory devices. In an embodiment, cache 1860 includes a write buffer that may improve interfacing efficiency by utilizing available data transport windows over an external signal path to receive write data and address/mask information. Once received, this information is temporarily stored in a write buffer until it is ready to be transferred to at least one memory device over interface 1820 b.

Computations circuit 1865 may include a processor or controller unit, a compression/decompression engine, etc., to further enhance the performance and/or functionality of buffer 100 a. In an embodiment, computations circuit 1865 controls the transfer of control/address/clock information and data between buffer interface 1103 a and interfaces 1820 a-c.

Clock circuit 1870 may include a clock generator circuit (e.g., Direct Rambus® Clock Generator), which may be incorporated onto buffer 101 a and thus may eliminate the need for a separate clock generating device.

In an alternate embodiment, clock circuit 1870 include clock alignment circuits for phase or delay adjusting an internal clock signal with respect to an external clock signal, such as a phase lock loop (“PLL”) circuit or delay lock loop (“DLL”) circuit. Clock alignment circuits may utilize an external clock from an existing clock generator, or an internal clock generator to provide an internal clock, to generate internal synchronizing clock signals having a predetermined temporal relationship with received and transmitted data and/or control information.

In an embodiment, clock circuit 1870 receives a first clock signal having a first frequency via signal path 121 and generates a second clock signal (via interface 1820 a) to memory device 101 a using the first clock signal and also generates a third clock signal (via interface 1820 a) to memory device 101 b using the first clock signal. In an embodiment, the second and third clock signals have a predetermined temporal (phase or delay) relationship with the first clock signal.

In an embodiment, a transmit circuit (such as in transceivers 1875, 1896 and 1894 shown in FIG. 18) transmits a differential signal that includes encoded clock information and a receiver circuit (such as in transceiver 1875, 1896 and 1894) receives a differential signal that includes encoded clock information. In this embodiment, a clock and data recovery circuit (such as clock circuit 1870) is included to extract the clock information encoded with the data received by the receiver circuit. Likewise, clock information may be encoded with data transmitted by the transmit circuit. For example, clock information may be encoded onto a data signal, by ensuring that a minimum number of signal transitions occur in a given number of data bits.

In an embodiment, a transceiver 1875 transmits and receives a first type of signal (for example, a signal having specified voltage levels and timing), while transceivers 1894 (and/or transmit circuit 1893) transmits and receives a second different type of signal. For example, transceiver 1875 may transmit and receive signals for a DDR2 memory device and transceivers 1894 may transmit and receive signals for a DDR3 memory device.

In an embodiment, the control information and/or data that is provided to buffer 100 a (by way of signal paths 121 and 120) may be in a different protocol format or have different protocol features than the control information and/or data provided to one or more memory devices 100 a-d from buffer 100 a. Logic (for example computation circuit 1865) in buffer 100 a performs this protocol translation between the control information and/or data received and transmitted. A combination of the different electrical/signaling and control/data protocol constitute an interface standard in an embodiment. Buffer 100 a can function as a translator between different interface standards—one for the memory module interface (for example connector interface 920) and another for one or more memory devices 100 a-d. For example, one memory module interface standard may require reading a particular register in a particular memory device disposed on the memory module. Yet, a memory module may be populated with memory devices that do not include the register required by the memory module interface standard. In an embodiment, buffer 100 a may emulate the register required by the memory module interface standard and thus allow for the use of memory devices 100 a-d that operate under a different interface standard. This buffer functionality, combined with the module topology and architecture, enables a memory module to be socket compatible with one interface standard, while using memory devices with a different interface standard.

In an embodiment, buffer 100 a includes a redundancy and repair circuit 1883 to test and repair the functionality of memory cells, rows or banks of a memory device, entire memory devices (or periphery circuits) and/or signal paths between buffer 100 a and memory devices 101 a-d. In an embodiment, redundancy and repair circuit 1883 periodically, during a calibration operation and/or during initialization, tests one or more of memory devices 101 a-d by writing a predetermined plurality of values to a storage location in a selected memory device (for example, using transceiver 1894 and a look-up table storing the predetermined values) using a selected data path and then reading back the stored predetermined plurality of values from the selected memory device using the selected data path. In an embodiment, when the values read from the storage location of the selected memory device do not match the values written to the storage location, redundancy and repair circuit 1883 eliminates access by buffer 100 a to the selected memory device and/or selected signal path. In an embodiment, a different signal path to a different memory device may be selected and this testing function may be performed again. If selecting the different signal path results in an accurate comparison of read predetermined values to the predetermined values in redundancy and repair circuit 1883 (or a pass of the test), the different memory address to a different memory location, within or to another memory device, is selected or mapped thereafter. Accordingly, future write and/or read operations to the defective memory location will not occur.

In an embodiment, any multiplexed combination of control information (including address information) and data intended for memory devices 101 a-d coupled with buffer 100 a is received via buffer interface 1103 a, which may, for example extract the address and control information from the data. For example, control information and address information may be decoded and separated from multiplexed data on signal path 120 a and provided on signal path 1895 to request and address logic circuit 1840 from buffer interface 1103 a. The data may then be provided to configurable serialization/deserialization circuit 1891. Request and address logic circuit 1840 generates one or more control signals to transmitter circuit 1893.

Interfaces 1820 a and 1820 b include programmable features in embodiments. A number of control signal lines and/or data signal lines between buffer 100 a and memory devices 101 a-d are programmable in order to accommodate different numbers of memory devices. Thus, more dedicated control signal lines are available with an increased number of memory devices. Using programmable dedicated control lines and/or data lines avoids any possible load issues that may occur when using a bus to transfer control signals between memory devices and a buffer 100 a. In another embodiment, additional data strobe signals for each byte of each memory device may be programmed at interface 1820 b to accommodate different types of memory devices, such as legacy memory devices that require such a signal. In still a further embodiment, interfaces 1820 a and 1820 b are programmable to access different memory device widths. For example, interfaces 1820 a and 1820 b may be programmed to connect to 16 “×4” width memory devices, 8 “×8” width memory devices or 4 “×6” width memory devices. Likewise, buffer interface 1103 a has a programmable width for signal path 120 a.

Configurable serialization/deserialization circuit 1891 performs serialization and deserialization functions depending upon a stored serialization ratio. As a memory device access width is reduced from its maximum value, memory device access granularity (measured in quanta of data) is commensurately reduced, and an access interleaving or multiplexing scheme may be employed to ensure that all storage locations within memory devices 101 a-d can be accessed. The number of signal paths 1006 may be increased or decreased as the memory device access width changes. Signal path 1006 may be subdivided into several addressable subsets. The address of the transaction will determine which target subset of signal path 1006 will be utilized for the data transfer portion of the transaction. In addition, the number of transceiver, transmitter and/or receiver circuits included in interfaces 1820 a and 1820 b that are employed to communicate with one or more memory devices 101 a-d may be configured based on the desired serialization ratio. Typically, configuration of the transceivers may be effectuated by enabling or disabling how many transceivers are active in a given transfer between one or more memory devices 101 a-d and buffer interface 1103 a. In an embodiment, a data rate of transferring data at buffer interface 1103 a is a multiple or ratio of a data rate of transferring data on one or more signal paths 1006 coupled to memory devices 101 a-d.

Buffer 100 a provides a high degree of system flexibility. New interface standards of memory devices may be phased in to operate with a master or a memory system that supports older interface standards by modifying buffer 100 a. In an embodiment, a memory module may be inserted using an older memory module interface or socket, while newer generation memory devices may be disposed on the memory module. Backward compatibility with existing generations of memory devices may be preserved. Similarly, new generations of masters, or controllers, may be phased in which exploit features of new generations of memory devices while retaining backward compatibility with existing generations of memory devices. Similarly, different types of memory devices that have different costs, power requirements and access times may be included in a single common package for specific applications.

FIG. 19 illustrates an integrated circuit memory device 1900 (or a memory die) in an embodiment. Integrated circuit memory device 1900 corresponds to one or more integrated circuit memory devices 101 a-d in embodiments. Integrated circuit memory device 1900 includes a memory core 1900 b and a memory interface 1900 a. Signal paths 1950 a-b, 1951 a-b, 1952 and 1953 are coupled to memory interface 1900 a. Signal paths 1950 a-b transfer read and write data. Signal paths 1951 a-b transfer address information, such as a row address and a column address in packets, respectively. Signal path 1952 transfers control information. Signal path 1953 transfers one or more clock signals. In an embodiment, signal paths 1950 a-b correspond to signal path 120 a shown in FIG. 10 and signal paths 1951 a-b, 1952 and 1953 correspond to signal path 121 in FIG. 10.

Memory interface 1900 a includes at least one transmitter and/or receiver for transferring signals between memory device 1900 and signal paths 1950 a-b, 1951 a-b, 1952 and 1953. Write demultiplexer (“demux”) 1920 and read multiplexer (“mux”) 1922 are coupled to signal path 1950 a, while write demux 1921 and read mux 1923 are coupled to signal path 1950 b. Write demux 1920-21 provide write data from signal paths 1950 a-b to memory core 1900 b (in particular sense amplifiers 0-2 a and 0-2 b). Read mux 1922-23 provide read data from memory core 1900 b to signal paths 1950 a-b (in particular sense amplifiers Na and Nb).

Demux and row packet decoder 1910 is coupled to signal path 1951 a and Demux and column packet decoder 1913 is coupled to signal path 1951 b. Demux and row packet decoder 1910 decodes a packet and provides a row address to row decoder 1914. Demux and Column packet decoder 1913 provides a column address and mask information to column and mask decoder 1915.

Control registers 1911 are coupled to signal path 1952 and provide control signals to row decoder 1914 and column and mask decoder 1915 in response to register values.

A clock circuit is coupled to signal path 1953 to provide a transmit clock signal TCLK and a receive clock signal RCLK in response to one or more clock signals transferred on signal path 1953. In an embodiment, write demux 1920 and 1921 provide write data from signal paths 1950 a-b to memory core 1900 b in response to an edge of receive clock signal RCLK. In an embodiment, read mux 1922 and 1923 provide read data from memory core 1900 b to signal paths 1950 a-b in response to an edge of a transmit clock signal TCLK. In an embodiment, the clock circuit generates a clock signal on signal path 1953 (to a buffer device) that has a temporal relationship with read data that are output on signal paths 1950 a-b.

Row decoder 1914 and column and mask decoder 1915 provide control signals to memory core 1900 b. For example, data stored in a plurality of storage cells in a memory bank is sensed using sense amplifiers in response to a row command. A row to be sensed is identified by a row address provided to row decoder 1914 from demux and row packet decoder 1910. A subset of the data sensed by a sense amplifier is selected in response to a column address (and possible mask information) provided by demux and column packet decoder 1913.

A memory bank in memory banks 0-N of memory core 1900 b includes a memory array having a two dimensional array of storage cells. In embodiments, memory banks 0-N include storage cells that may be DRAM cells, SRAM cells, FLASH cells, ferroelectric RAM (“FRAM”) cells, magnetoresistive or magnetic RAM (“MRAM”) cells, or other equivalent types of memory storage cells. In an embodiment, integrated circuit memory device 1900 is a DDR integrated circuit memory device or later generation memory device (e.g., DDR2 or DDR3). In an alternate embodiment, integrated circuit memory device 1900 is an XDR™ DRAM integrated circuit memory device or Direct Rambus® DRAM (“DRDRAM”) memory device. In an embodiment, integrated circuit memory device 1900 includes different types of memory devices having different types of storage cells housed in a common package.

FIGS. 20A-B illustrate signal paths between memory module interface portions and a plurality of integrated circuit buffer devices. In particular, FIG. 20A illustrates how each buffer device 100 a-d has signal paths for data signals coupled to each connector interface portion 920 a-h. In an embodiment, FIGS. 20A-B illustrate signal paths between buffer devices and connector interfaces of memory module 900 that include a plurality of memory devices as shown in FIGS. 9A-C. For example, FIG. 20B which shows an expanded section of FIG. 20A, illustrates how data signal paths 2003 and 2004 provide data signals between connector interface portions 920 a and 920 e and buffer device 100 a. FIG. 20A also illustrates how signal paths for control/address signals, such as control/address signal paths 2001 and 2002, couple connector interface portions 930 a and 930 b to buffer devices 100 a-d. In an embodiment, each signal path 2001 and 2002 is a multi-drop bus as shown in FIG. 1.

FIGS. 21A-D illustrate memory system point-to-point topologies including a master 2101 and at least one memory module having a plurality of integrated circuit memory devices (The plurality of memory devices on respective memory modules are not illustrated in FIGS. 21A-D, 22A-C, 23A-C and 24A-B for clarity). In an embodiment, FIGS. 21A-D, 22A-C, 23A-C and 24A-B illustrate signal paths between memory modules, such as memory module 900 as shown in FIGS. 9A-C, and other memory modules and/or masters. FIGS. 21A-D illustrate expanding memory capacity and bandwidth as well as different configurations. In particular, master 2101 is coupled to interfaces (such as sockets) 2102 and 2103 by signal paths 2120, 2121 a-b, 2122 and 2123 in Dynamic Point-to-Point (“DPP”) system 2100 a. In an embodiment, master 2101, interfaces 2102 and 2103 as well as signal paths 2120, 2121 a-b, 2122 and 2123 are disposed on a substrate, such as a printed circuit board (“PCB”). In an embodiment, memory modules may be inserted and/or removed (unpopulated) from interfaces 2102 and 2103. In an embodiment, signal paths 2120, 2121 a-b, 2122 and 2123 are signal traces on a PCB. In an embodiment, signal paths 2120 and 2121 a-b provide data between data signal paths on a memory module, such as signal paths 120 a and 120 b shown in FIG. 1, and master 2101. In an embodiment, signal paths 2122 and 2123 provide control/address information to the memory modules (via interfaces 2102 and 2103 and in particular connector interface portions 930 b of the memory modules) from master 2101. In particular, control/address information is provided from signal paths 2122 and 2123 to a signal path on the memory modules, such as signal path 121 shown in FIG. 1.

FIG. 21A illustrates a DPP system 2100 a that simultaneously accesses two buffer devices in memory modules coupled to interfaces 2102 and 2103. In response to control and address information provided on signal paths 2122 and 2123 from master 2101, the two buffers 101 a output data simultaneously from connector interface portions 920 a and 920 e, respectively, onto signal paths 2120 and 2121 a, that are coupled to master 2101. In an embodiment, signal paths 2120 and 2121 a are point-to-point links. In an embodiment, a point-to-point link includes one or a plurality of signal lines, each signal line generally having two transceiver connection points, each transceiver connection point coupled to a transmitter circuit, receiver circuit or transceiver circuit. For example, a point-to-point link may include a transmitter circuit coupled at or near one end and a receiver circuit coupled at or near the other end. The point-to-point link may be synonymous and interchangeable with a point-to-point connection or a point-to-point coupling.

In an embodiment, the number of transceiver points along a signal line may distinguish between a point-to-point link and a bus. For example, a point-to-point link generally includes only two transceiver connection points while a bus generally includes more than two transceiver points. In some instances a point to point link can be mixed with bussed signal lines, where the bussed single lines may be used to provide sideband functionality such as maintenance, initialization or test.

Several embodiments of point-to-point links include a plurality of link topologies, signaling, clocking and signal path types. Embodiments having different link architectures include simultaneous bidirectional links, time-multiplexed bidirectional links and multiple unidirectional links. Voltage or current mode signaling may be employed in any of these link topologies.

FIG. 21B illustrates a DPP with Continuity Module system 2100 b for accessing a buffer device 101 a in a memory module coupled to interface 2103 while a continuity memory module 2105 is coupled to interface 2102. In an embodiment, master 2101 outputs a single set of control/address information on signal paths 2122 and 2123. Data is output from connector interfaces 920 a and 920 e of the memory module coupled to interface 2103 in response to the single set of control/address information. Data is provided to master 2101 on signal path 2120 via signal path 2121 b and a bypass circuit in continuity memory module 2105. The bypass circuit passes the data from connector interface portion 920 e to connector interface portion 920 a in continuity memory module 2105. Data is also provided to master 2101 by signal path 2121 a.

FIG. 21C illustrates a DPP bypass system 2100 c similar to system 2100 b except that a buffer device 101 a (rather than continuity memory module 2105) in a memory module includes a bypass circuit for passing the data from connector interface portion 920 e to connector interface portion 920 a of the memory module inserted in interface 2102.

FIG. 21D illustrates a DPP bypass system 2100 d similar to system 2100 c except that data is accessed from buffer device 101 a of the memory module coupled to interface 2102 and buffer device 101 a of the memory module coupled to interface 2103 includes a bypass circuit for passing the data from connector interface portion 920 a to connector interface portion 920 e.

In an embodiment, a clock signal or clock information is provided on signal paths 2122 and 2123, on a separate signal path from a clock source or master 2101, or along the data signal paths 2121 a-b.

FIGS. 22A-C illustrate memory system daisy chain topologies including a master 2101 and at least one memory module having a plurality of integrated circuit memory devices. In particular, FIGS. 22A-C illustrate how half of the bandwidth, as compared to system 2100 a-d, is obtained when accessing a single memory module in an embodiment. FIG. 22A illustrates a Daisy Chain system 2200 a that includes a buffer 101 a in a memory module coupled to interface 2103 that provides data (by way of connector interface portion 920 e) on signal path 2121 a in response to a single set of control/address information output by master 2101 onto signal paths 2122 and 2123. No module is coupled to interface 2102.

FIG. 22B illustrates a Daisy Chain system 2200 b that is similar to system 2200 a except a memory module is coupled to interface 2102.

FIG. 22C illustrates a Daisy Chain system 2200 c similar to system 2200 b except that data accessed from a buffer device 101 a in a memory module is coupled to interface 2102 rather than interface 2103. Buffer device 101 a in a memory module coupled to interface 2103 provides a bypass circuit to allow data to be received at interface portion 920 a and output at interface portion 920 e of the memory module coupled to interface 2103. Data is thus passed from data path 2121 b to data path 2121 a and ultimately to master 2101.

FIGS. 23A-C and 24A-B illustrate memory system topologies including a master to provide control/address information to a plurality of integrated circuit buffer devices. In particular, FIG. 23A illustrates a Dedicated/Fly-by system 2300 a that includes a master 2101 that provides control/address information to memory modules 2301 a and 2301 b (in particular to integrated circuit buffer devices 101 a-d on each memory module) by signal paths 2311 and 2310, respectively. In an embodiment, signal paths 2310 and 2311 are separate and carry control/address information for each respective memory module. In an embodiment, signal path 2311 does not pass through or include a signal path in memory module 2301 b. In an embodiment, signal path 2311 does not pass through or include an interface, such as a socket, used for memory module 2301 b. The double headed arrow in FIGS. 23A-C, 24A-B and 25A-B illustrate the data information (read and write data) transferred on separate data paths between memory modules 2301 a-b (and in particular from buffer devices) and master 2101. In an embodiment, a clock signal or clock information is provided on signal paths 2310 and 2311, on a separate signal path from a clock source or master 2101, or along the data signal paths.

Signal path 2311 is terminated by termination 2350 a and signal path 2310 is terminated by termination 2350 b. In an embodiment, the impedance of termination 2350 a matches the impedance of a portion of the signal path 2311 (multi-drop bus 2320 a) on memory module 2310 a, (Z0) and the impedance of termination 2350 b approximately matches the impedance of a portion of the signal path 2310 (multi-drip bus 2320 b) on memory module 2301 b (Z1). In an embodiment, impedance Z0 approximately equals impedance Z1. In embodiments, terminations 2350 a and 2350 b, singly or in combination, are disposed on memory module, buffer devices or packages used to house buffer devices. FIG. 23B illustrates a Stub/Fly-by system 2300 b similar to system 2300 a except that a single signal path 2320 provides control/address information from master 2101 to memory modules 2301 a and 2301 b (in particular to integrated circuit buffer devices 101 a-d on each memory module). In an embodiment, memory modules 2301 a and 2301 b include stubs/internal signal paths (multi-drop bus) 2320 a-b coupled to a single common signal path 2320 that are disposed on memory modules 2301 a-b. In an embodiment, a portion of signal path 2320 passes through or includes an interface, such as a socket, used for memory module 2301 b. Memory modules 2301 a and 2301 b are terminated similar to system 2300 a.

FIG. 23C illustrates a Serpentine system 2300 c similar to system 2300 a except that a single signal path 2320 provides control/address information from master 2101 to memory modules 2301 a and 2301 b (in particular to integrated circuit buffer devices 101 a-d on each memory module) without using stubs on respective memory modules as illustrated in FIG. 23B. In an embodiment, a single signal path 2330 couples master 2101 to memory modules 2301 a and 2301 b. In an embodiment signal path 2330 includes a first external signal path portion between master 2101 and memory module 2301 b; a second signal path portion disposed on the memory module 2301 b and coupled to the first signal path portion as well as to respective buffer devices 101 a-d; a third external signal path portion 2331 coupled to the second signal path portion and also coupled to memory module 2301 a; and a fourth signal path portion disposed on the memory module 2301 a and coupled to the third signal path portion 2331 as well as to respective buffer devices 101 a-d on memory module 2301 a. Termination 2350 a, in an embodiment, is not disposed on memory module 2301 a in order to ensure that memory modules are interchangeable. Termination 2350 a may be disposed on a PCB or elsewhere in a system.

FIG. 24A illustrates a Dedicated/Tree system 2400 a similar to system 2300 a except that memory modules 2401 a-b include buffer devices 101 a-d that are coupled by way of a tree structure signal path 2413. In particular, memory module 2401 a is coupled to signal path 2311 by signal path 2413 a disposed on memory module 2401 a that then branches in to signal paths 2413 b and 2413 c. Signal path 2413 b then is coupled to buffer devices 101 a and 101 b by branches or signal paths 2413 d and 2413 e. Signal path 2413 c, likewise, is coupled to buffer devices 101 c and 101 d by branches or signal paths 2413 f and 2413 g. In an embodiment, memory module 2401 b has a similar tree structure signal path 2413 to couple buffer devices 101 a-d to signal path 2310.

FIG. 24B illustrates a Stub/Tree system 2400 b similar to system 2400 a shown in FIG. 24A that includes tree structure signal path 2413 in memory modules 2401 a-b. System 2400 b illustrates signal path 2320 including stubs/signal paths 2320 a and 2320 b that couple master 2101 to memory modules 2401 a and 2401 b, respectively. Stub/signal path 2320 a is coupled to signal path 2413 a disposed on memory module 2401 a and stub/signal path 2320 b is coupled to signal path 2413 a disposed on memory module 2401 b.

In embodiments, termination may be disposed on buffers 101 a-d, memory modules 2401 a-b and/or elsewhere in a system, such as on a PCB.

FIGS. 25A-B illustrate memory modules having different memory capacity or different sized address spaces. In particular, memory module address space 2501 on a first memory module is larger than memory module address space 2502 on a second memory module. In an embodiment, memory module address space 2501 is twice as large as memory module address space 2502. For example, memory module address space 2501 may store 2 gigabyte (GB) of information and memory module address space 2502 may store 1 GB of information. Increasing the number or density of integrated circuit memory devices disposed on a memory module may increase address space.

FIG. 25A illustrates how half (or portion) of the available signal path width, for example half of a bus width, is used to access the first half of memory module address space 2501 (overlapping address space) while the other half of the available signal path width is used to access memory module address space 2502.

FIG. 25B illustrates how a larger capacity memory module is able to use a full signal path by accessing a first half (or portion) of the available signal path width coupled directly to the larger capacity memory module and by way of accessing a second half (or portion) of the available signal path width coupled to the smaller capacity memory module using bypassing through the smaller capacity memory module. FIGS. 26-29 illustrate how non-overlap address space of a larger memory module may be accessed in various embodiments.

FIGS. 26A-B illustrate a system 2600 to access different sized/capacity (address space) memory modules during different modes of operation, a first mode of operation and a second mode of operation (or bypass mode). System 2600 includes a master 2101 coupled to memory module 2601 by signal path 2610 and memory module 2602 by signal path 2612. Memory modules 2601 and 2602 are coupled by signal path 2611. In an embodiment, memory modules 2601 and 2602 represent memory modules including integrated circuit memory devices and buffer devices as described herein. In an embodiment, memory module 2601 has a larger address space than memory module 2602. In an embodiment, signal paths 2610-2612 are point-to-point links that provide read/write data. In embodiments, control/address/clock information is provided on separate signal paths as described herein. Memory modules 2601 and 2602 may include bypass circuits 2630 a-b.

In a first mode of operation (or a non-bypass mode) illustrated in FIG. 26A, read data 2601 a (stored in an overlapping address space) is provided on signal path 2610 to master 2101 from memory module 2601 in response to control/address information provided by master 2101 to memory module 2601. Similarly, read data 2602 a (stored in an overlapping address space) is provided on signal path 2612 to master 2101 from memory module 2602 in response to control/address information provided by master 2101 to memory module 2602. In the first mode of operation, signal path 2611 is not used.

In a second mode of operation (or a bypass mode) illustrated in FIG. 26B, read data 2601 b (stored in a non-overlapping address space of memory module 2601) is provided on signal path 2610 to master 2101 from memory module 2601 in response to control/address information provided by master 2101 to memory module 2601. Read data 2601 c (stored in a non-overlapping address space of memory module 2601) is provided on signal path 2611 to memory module 2602 in response to control/address information provided by master 2101 to memory module 2601. Bypass circuit 2630 b then provides read data 2601 c to signal path 2612 and eventually to master 2101.

Write data from master 2101 may be provided to memory modules 2601 and 2602 similar to how read data is obtained during a first and second mode of operation.

In embodiments, modes of operation are determined in response to a control signal from master 2101, or other circuit or in response to reading configuration information stored in a separate storage circuit in a device, such as an SPD device or register on the buffer or controller device, disposed on system 2600. Modes of operation may be determined at initialization, periodically or during calibration of system 2600.

In embodiments, bypass circuits 2630 a-b (as well as bypass circuits 2630 c-d shown in FIG. 27) correspond to bypass circuit 2900 as described below and shown in FIG. 29 and/or bypass circuit 1898 shown in FIG. 18. In embodiments, these bypass circuits can be incorporated on the buffer devices on the module.

FIG. 27 illustrates a system 2700 including master 2101 coupled to at least four memory modules 2701-2704 by way of interfaces 2701 a-d. In an embodiment, interfaces 2701 a-d are female sockets disposed on a substrate, such as a backplane, motherboard or PCB, to receive male edge interfaces of memory modules 2701-2704. In an embodiment, memory modules 2701-2704 represent memory modules including integrated circuit memory devices and buffer devices as described herein as well as at least one of bypass circuits 2630 a-d.

Master 2101 is coupled to memory module 2701 by signal path 2710. Signal path 2711 couples memory module 2701 to memory module 2704. In an embodiment, bypass circuit 2630 a allows read and write data to be transferred between signal paths 2711 and 2710 either to or from master device 2101 in response to control/address information provided to memory module 2704.

Master 2101 is coupled to memory module 2702 by signal path 2712. Signal path 2713 couples memory module 2702 to memory module 2703. Signal path 2714 couples memory module 2703 to memory module 2704. In an embodiment, bypass circuits 2630 b and 2630 c allow read and write data to be transferred between signal paths 2712 and 2713, as well as signal paths 2713 and 2714, either to or from master device 2101 in response to control/address information provided to memory modules 2702-04.

Master 2101 is coupled to memory module 2703 by signal path 2714. Signal path 2716 couples memory module 2703 to memory module 2704. In an embodiment, bypass circuit 2630 c allows read and write data to be transferred between signal paths 2714 and 2716 either to or from master device 2101 in response to control/address information provided to memory modules 2703-04.

Master 2101 is coupled to memory module 2704 by signal path 2717. In an embodiment, read and write data is transferred on signal path 2717 to or from master device 2101 in response to control/address information provided to memory module 2704.

FIGS. 28A-B illustrate a system 2700 to access different capacity/sized (address space) memory modules during different modes of operation that is similar in operation to that of system 2600. FIG. 28A illustrates accessing data in a first mode of operation, such as accessing read data from different sized memory modules that may be disposed in interfaces 2701 a-d. Table 2810 illustrates how different sized memory modules may be disposed in respective interfaces 2701 a-d during a first mode of operation. For example, interfaces 2701 a-d may be coupled to all “small” sized memory modules as indicated by the first row of Table 2810. Alternatively, interface 2701 a may be coupled to a “large” sized memory module; interface 2701 b may be coupled to a “small” sized memory module; interface 2701 c may be coupled to a “large” sized memory module; and interface 2701 d may be coupled to a “small” sized memory module, as indicated by the second from last row of Table 2810.

In a first mode of operation (non-bypass mode) as illustrated by FIG. 28A, data 2810 a is provided on signal path 2717; data 2820 a is provided on signal path 2714; data 2830 is provided on signal path 2712; and data 2840 is provided on signal path 2710.

Table 2820 illustrates how different sized memory modules may be disposed in respective interfaces 2701 a-d during a second mode of operation (bypass mode). For example, interfaces 2701 c-d may be coupled to “small” sized memory modules and interfaces 2701 a-b include bypass circuits 2802 and 2801 as indicated by the first row of Table 2820. Alternatively, interface 2701 c may be coupled to a “large” sized memory module; and interface 2701 d may be coupled to a “small” sized memory module. Interfaces 2701 a-b include bypass circuits 2802 and 2801, as indicated by Table 2820.

In a second mode of operation (bypass mode) as illustrated by FIG. 28B, read data 2810 b is provided on signal path 2717 and read data 2810 c is provided on signal paths 2711 and 2710 (via bypass circuit 2802). Read data 2820 b is provided on signal path 2714 and read data 2820 c is provided on signal paths 2713 and 2712 (via bypass circuit 2801).

In embodiments, bypass circuits 2801 and/or 2802 are disposed in a continuity module, integrated circuit buffer device, interface (for example a socket) and/or memory module. In an embodiment, bypass circuits 2801 and 2802 are conductive elements, such as metal traces or wires that may be disposed manually on an interface or memory module. In an embodiment, bypass circuits 2801 and 2802 correspond to bypass circuit 2900 shown in FIG. 29.

FIG. 29 illustrates a bypass circuit 2900 used in a write operation according to an embodiment. Bypass circuit 2900 includes receiver and transmitter circuits 2901 a-e and 2902 a-d coupled to a signal path including signal paths DQ[0:3] and RQ. In an embodiment, bypass circuit 2900 is included in an integrated circuit buffer device, such as corresponding to bypass circuit 1898 in buffer interface 1103 a, disposed on a memory module and/or corresponding to bypass circuits 2630 a-d shown in FIGS. 26A-B and 27. For example, signal paths DQ[0:1] are coupled to connector interface portion 920 a and signal paths DQ[2:3] are coupled to connector interface portion 920 b as shown in FIGS. 20A-B. In an embodiment, signal paths DQ[0:1] are coupled to an adjacent master or memory module and signal paths DQ[2:3] are coupled to a memory module in a memory system.

Receiver circuits 2901 a-d receive write data signals from signal paths DQ[0:3] and provide write data to data width translator circuit 2950 and/or back out to a signal path by way of transmitters 2902 a-d and bypass elements 2905-2910. Receiver circuit 2901 e receives write address signals from signal path RQ and provides write addresses to data width translator circuit 2950. Receiver circuit 2901 a is coupled to bypass elements 2906 and 2908 to reroute received data signals to transmitter circuits 2902 b and 2902 c in response to control signals (not shown) provided to bypass elements 2906 and 2908. Receiver circuit 2901 b is coupled to bypass elements 2905 and 2910 to reroute received data signals to transmitter circuits 2902 a and 2902 d in response to control signals (not shown) provided to bypass elements 2905 and 2910. Receiver circuit 2901 c is coupled to bypass element 2907 to reroute received data signals to transmitter circuit 2902 a in response to control signals (not shown) provided to bypass element 2907. Receiver circuit 2901 d is coupled to bypass element 2909 to reroute received data signals to transmitter circuit 2902 b in response to control signals (not shown) provided to bypass element 2909.

As can be seen, write data may be rerouted from a single signal path DQ0 to another single signal path DQ1. Write data may be also rerouted from two signal paths DQ0 and DQ1 to signal paths DQ2 and DQ3.

In an embodiment, bypass elements 2905-2910 function independently as respective switches to allow a signal (represented by a voltage level) to be passed from a receiver circuit to a transmitter circuit. In an embodiment, bypass elements 2905-2910 are semiconductors such as negative and/or positive-channel metal-oxide (NMOS/PMOS) semiconductors with a control signal (such as a voltage) provided to a gate of the semiconductor while a source and/or a drain is coupled to a transmitter and/or receiver circuit. In an alternate embodiment, other types of semiconductors or switches may be used. In an embodiment, control signals (not shown) provided to bypass elements 2905-2910 are provided by master 2101 or from a programmable register, such as an SPD device. In an embodiment, control signals are provided by a master after reading memory capacity information of memory modules stored in one or more SPD devices. In an embodiment, control signals provided to bypass elements may be provided in response to a manual jumper, programmable fuse or register. In an embodiment, control signals provided to bypass elements may be provided by one or more integrated circuit buffer devices in response to one or more integrated circuit buffer devices reading a received address/control information. For example, when an address is received that identifies a memory location that is not provided on a particular memory module (non-overlapping address space or smaller capacity memory module), control signals are provided to bypass elements from the integrated circuit buffer device that received the address/control information (in a bypass mode) to enable data to be rerouted from the larger capacity memory module to another destination, such as a master.

In an embodiment, bypass elements 2905-2910 may be disposed before or left of receiver and transmitter circuits 2901 a-d and 2902 a-d as well as in or after (right of) data width translator circuit 2950 (for example, after a clock barrier or boundary). Bypass elements 2905-2910 may be disposed in a master, an interface (such as a socket) and/or a memory module (outside of a buffer device). Bypass elements 2905-2910 may also be disposed internal to an integrated circuit buffer, as opposed to an interface of an integrated circuit buffer device, or in an integrated circuit memory device.

In an embodiment, rerouted write data may be resynchronized by a transmitter circuit using a different or the same clock signal that is used by the receiver circuit in receiving the read data. Also, write data that has been rerouted by bypass elements may be transmitted in a fast analog mode.

Stored read data from integrated circuit memory devices disposed on a memory module are provided on signal paths DQ_DRV[0:3] by way of an integrated circuit buffer device. Read data is levelized or delays are provided to the read data by a selector circuit, such as multiplexers (mux) 2903 a-d, and delay circuits 2904 a-d in response to DELAY[0:3] control signals. Signal paths DQ_DRV[0:3] are input to delay circuits 2904 a-d and a first input (“0 input”) of mux 2903 a-d, while an output of delay circuits 2904 a-d is provided to a second input (“1 input”) of mux 2903 a-d. DELAY[0:3] control signals select an output of mux 2903 a-d or whether a delay is introduced into read data on signal paths DQ_DRV[0:3]. In an embodiment, delay circuits 2904 a-d may introduce a programmable delay in response to a control signal (not shown). Control signals provided to delay circuits 2904 a-d as well as DELAY[0:3] control signals may be provided similar to control signals provided to bypass elements 2905-2910 as described above.

In an embodiment, delay circuits 2904 a-d are inventers, registers and/or a series of inventers and/or registers that may introduce programmable delay to a read signal on signal paths DQ_DRV[0:3]. The amount of delay provided to read data by delay circuits 2904 a-d may be longer than the amount of time for providing read data to delay circuits 2904 a-d, or longer than a data cycle time.

In an embodiment, multiplexers 2903 a-d and delay circuits 2904 a-d may be disposed before or left of receiver and transmitter circuits 2901 a-d and 2902 a-d. For example, multiplexers 2903 a-d and delay circuits 2904 a-d may be disposed in a master, interface (such as a socket) and/or memory module. In an embodiment, multiplexers 2903 a-d and delay circuits 2904 a-d may be disposed in data width translator circuit 2950 and/or left of data width translator circuit 2950. For example, multiplexers 2903 a-d and delay circuits 2904 a-d may be disposed internal to an integrated circuit buffer, as opposed to an interface of an integrated circuit buffer device, or in an integrated circuit memory device.

Levelization or the amount of delay (if any) provided to read data on signal paths DQ_DRV[0:3] is dependent upon the signal path (between a memory module and a master) used by a system to provide the read data to the master (or flight time or amount of time to transfer read data from a memory module to a master and/or another memory module). For example in a system 2600 shown in FIG. 26B, delay is introduced into data 2601 b so that data 2601 b arrives at master 2101 at the approximate same time data 2601 c arrives at master 2101 because data 2601 c travels a longer path (as compared to data 2601 b) on signal paths 2611 and 2612 as well as through memory module 2602 (or at least through an integrated buffer device/interface of memory module 2602).

Data width translator circuit 2950 may be configurable to translate data of various widths into data suitable for a fixed-width memory die or device disposed on a memory module. Data width translator circuit 2950, in accordance with some embodiments, uses a data-mask signal to selectively prevent memory accesses to subsets of physical addresses. This data masking divides physical address locations of the memory die into two or more temporal subsets of the physical address locations, effectively increasing the number of uniquely addressable locations in a particular memory die. As used herein, the term “width” refers to the number of bits employed to represent data.

A data width translator circuit 2950 allows memory modules, such as memory modules 2601 and 2602, to vary the effective width of their external memory module interfaces without varying the width of the internal memory device/die interfaces. A memory system thus may support a first mode of operation and a second mode of operation (bypass mode). In the bypass mode of operation, memory module 2601 uses both signal path 2610 and signal paths 2611 and 2612 (via memory module 2602).

In accordance with an embodiment, data width translator circuit 2950 can translate data of width one, two, or four on signal paths DQ[0:3] into four-bit-wide data on signal path IDQ[0:3]. Address translator circuit 2970 translates address signals on signal path RQ to signal path IRQ which is coupled to one or more memory devices. This flexibility allows one or a combination of memory modules to be used in an extensible point-to-point memory topology. Similarly, data width translator circuit 2950 can translate data of width one, two, or four on signal paths IDQ[0:3] into four-bit-wide data on signal path DQ[0:3].

Data width translator circuit 2950 includes a data translator circuit 2960, an address translator circuit 2970, and a DLL 2980. DLL 2980 produces an internal differential clock signal ICLK locked (or having a temporal relationship) to a like-identified incoming differential clock signal CLK, typically from an associated master or a clock-generator device. Though not shown, a memory device disposed on a memory module may receive the same or a similar clock signal CLK from data width translator circuit 2950 or a master. Data translator circuit 2960 and address translator circuit 2970, responsive to a configuration signal CFG, translate the data on one, two, or four of data signal paths DQ[0:3] into four-bit-wide data on signal paths IDQ[0:3] for write cycles; and conversely translate four-bit-wide data on signal paths IDQ[0:3] into one, two, or four-bit-wide data on one or more of external signal paths DQ[0:3] for read cycles. In one embodiment, plugging a second memory module into a two-connector mother board automatically asserts configuration signal CFG, causing each of two memory modules to configure themselves as half-width (e.g., two bits instead of four) modules. In other embodiments, configuration signal CFG comes from a register on a memory module (e.g., within data width translator circuit 2950) that is addressable by a master and is set, such as via the BIOS, at boot time. In other embodiments, a configuration signal CFG is provided after reading values stored in a SPD device. In general, an external memory module interface conveys data signals of data-width N, an internal memory device interface conveys signals of data-width M, and configuration signal CFG is indicative of the ratio of N to M. Some embodiments use a PLL instead of DLL 2980.

A fixed-width memory device disposed on a memory module may include a mask line/signal path or pin that can be used in support of partial-write operations. For example, double data rate “DDR” memory die include a data-mask pin DM and single data rate “SDR” memory die include a data-mask pin DQM. Memory modules detailed herein may employ data-mask functionality to create variable-width modules using fixed-width memory devices. In an embodiment, a data-mask signal DM is output from data translator circuit 2960 to one or more memory devices in order to synchronize write operations. FIGS. 30A-B, described below, illustrate a write operation using data width translator circuit 2950 in an embodiment.

In an embodiment, bypass circuit 2900 includes bypass elements 2905-2910 and not multiplexers 2903 a-d and delay circuits 2904 a-d. In an alternate embodiment, bypass circuit 2900 includes multiplexers 2903 a-d and delay circuits 2904 a-d and not bypass elements 2905-2910. For example, memory module 2601 shown in FIG. 26B, and in particular bypass circuit 2630 a, may include multiplexers 2903 a-d and delay circuits 2904 a-d to provide a delay to data 2601 a and not bypass elements 2905-2910. Conversely, memory module 2602, and in particular bypass circuit 2630 b, may include bypass elements 2905-2910 to reroute data 2601 c but not multiplexers 2903 a-d and delay circuits 2904 a-d to provide a delay. In an embodiment, bypass circuit 2900 is disposed in a memory system that does not include an integrated circuit buffer device.

FIGS. 30A-B illustrate a pair of timing charts 3000 and 3001 depicting the operation of a memory system, or memory module, using data width translator circuit 2950 in a first mode of operation and a second mode of operation (bypass mode). Data to be written to a common address A in a single memory device disposed on a memory module may be transmitted over external signal paths DQ[0:3] as four eight-symbol bursts (a single eight-symbol burst 0A-0H on signal path DQ0 is shown in FIG. 30B) and an address A on signal path RQ. For example, signal path DQ0 conveys eight binary symbols 0A through 0H for storage at physical address location A in a fixed width memory device on the memory module. In embodiments, the three remaining signal paths DQ[1:3] likewise may convey eight symbols for storage at address location A. When all signal paths DQ[0:3] are used, the total number of symbols to be stored at a given address A may be thirty-two (four times eight). Data width translator circuit 2950 may convey the thirty-two symbols and corresponding address A to a memory device via signal paths IDQ[0:3] and IRQ. The burst length can be longer or shorter in other embodiments.

In an embodiment, data width translator circuit 2950 uses mask signal DM to divide the addressed physical locations in a fixed-width memory device into subsets of memory locations addressed separately in the time domain, a process that may be referred to as “time slicing.” For example, a most significant bit(s) (MSB(s)), or any other bits in address A, causes data translator circuit 2960 (via a signal from address translator circuit 2970 to data translator circuit 2960) to assert a mask signal DM (DM=1) to block writes to a first set of locations having address A, and then de-asserts mask signal DM (DM=0) to allow writes to the second set of locations having address A. This process then may repeat.

FIG. 30A illustrates how data provided from two external signal paths DQ[0:1] is output on signal paths IDQ[0:3] by data width translator circuit 2950 in a bypass mode of operation (i.e. memory modules 2701 and 2702 are bypassed as illustrated in FIGS. 27 and 28B). In an embodiment, signal path DQ0 is included in signal path 2717 and signal path DQ1 is included in signal path 2711. Data 0A-0H is provided on signal path 2717 from master 2101 while data 1A-1H is also provided by master 2101 on signal path 2711 via memory module 2701 and signal path 2710.

In an embodiment, the address space in memory module 2704 (i.e. memory devices) is bisected in the time domain. One of the external address bits of address A is employed to assert mask signal DM every other time slot. In this embodiment, the MSB of the external address A is zero, so mask signal DM is deasserted for every time slot MSB=0 to allow writes during those time slots.

FIG. 30B illustrates how data provided from an external signal path DQ0 (or signal paths DQ[0:3]) is output on signal paths IDQ[0:3] by data width translator circuit 2950 in a non-bypass mode of operation (i.e. data is provided to each of the memory modules/sockets as illustrated in FIGS. 27 and 28A). In an embodiment, signal path DQ0 is included in signal path 2717. Data 0A-0H is provided on signal path 2717 from master 2101. Similarly, other data may be provided from master 2101 to memory modules 2701-2703 on signal paths DQ1, DQ2 and DQ3 that are included in signal paths 2710, 2712 and 2714.

FIG. 31 illustrates a method 3100 to adjust read and write data delays in a system including memory modules having different capacity and a bypass circuit. In embodiments, logic blocks illustrated in FIG. 31 are carried out by hardware, software or a combination thereof. In embodiments, logic blocks illustrated in FIG. 31 illustrate actions or steps. In embodiments, the circuits and/or systems illustrated herein, singly or in combination, carry out the logic blocks illustrated in FIG. 31. Other logic blocks that are not shown may be included in various embodiments. Similarly, logic blocks that are shown may be excluded in various embodiments. Also, while method 3100 is described in sequential logic blocks, steps or logic blocks of method 3100 are completed very quickly or almost instantaneously.

Method 3100 begins at logic block 3101 where a determination is made whether to levelize or adjust delays to read and write data in a memory system. In an embodiment, this determination may be made at initialization, periodically or during calibration (testing). If levelization is not desired, method 3100 ends. Otherwise, integrated circuit buffer devices are set to a typical or first mode of operation as illustrated by logic block 3102. In an embodiment, a control signal from a master, such as master 2101 shown in FIG. 26A-B, generates a control signal to memory modules, and in particular to integrated circuit buffer devices of the memory modules to operate in a first mode of operation which includes providing read and write data on separate signal paths (signal paths 2610 and 2612) to or from a master as illustrated in FIG. 26A. In the first mode of operation, no additional delay is provided to read and write data, as compared to the second mode of operation described below.

Logic block 3103 illustrates levelizing read data or providing delays to read data to take into account different flight times or distances the read data must travel on different signal paths in reaching a master. For example, signal path 2612 has a longer signal path than signal path 2610. Therefore, in order for read data 2601 a and 2602 a from both memory modules 2601 and 2602 to reach master 2101 at the approximate same time, a delay should be introduced into the read data 2601 a to account for the longer flight time or distance of signal path 2612. In an embodiment, delays are provided in response to delay values stored in registers on the integrated circuit memory devices and programmed by the master. In alternate embodiments, delays corresponding to respective memory modules are provided and programmed in the master. Test symbols or test data may be written and read from the integrated circuit memory devices to determine the programming of the delay values.

A determination is then made whether a memory system includes different capacity memory modules as illustrated by logic block 3104. If different capacity memory modules are not present, control transitions to logic block 3107. Otherwise, control transitions to logic block 3105. In an embodiment, the determination illustrated by logic block 3104 may be completed by a master reading configuration information of a system stored in an SPD.

Integrated circuit buffer devices are then set to a second mode of operation (bypass mode) as illustrated in logic block 3105. In an embodiment, the bypass mode of operation is set by providing control signals to a bypass circuit in an integrated circuit buffer device, for example bypass elements 2905-2910 in a bypass circuit 2900 as illustrated in FIG. 29.

Read data from a larger capacity memory module is then levelized as illustrated by logic block 3106. For example, delays are added to read data 2601 b of memory module 2601 (larger capacity) as illustrated in FIG. 26B. In an embodiment, Delay[0:3] control signals are provided to multiplexers 2901 a-d to select additional delay to data signal on signal path DQ_DRV[0:3] of bypass circuit 2900 shown in FIG. 29. The delay provided in logic block 3106 is in addition to any delay provided in logic block 3103.

Integrated circuit buffers in a smaller capacity memory module are set to a first mode of operation (or a non-bypass mode) as illustrated by logic block 3109. For example, memory module 2602 in FIG. 26A has an integrated circuit buffer device that is set to a typical mode of operation.

Read data levelization for the smaller capacity memory module is then performed as illustrated by logic block 3108.

Write data levelization for data written to memory modules is performed in logic block 3107.

A determination is then made whether a memory system includes different capacity memory modules as illustrated by logic block 3110. If different capacity memory modules are not present, method 3100 ends. Otherwise, control transitions to logic block 3111. In an embodiment, the determination illustrated by logic block 3110 may be completed by a master reading configuration information of a system stored in a SPD.

Integrated circuit buffer devices are then set to a second mode of operation (bypass mode) as illustrated in logic block 3111. In an embodiment, the bypass mode of operation is set by providing control signals to a bypass circuit in an integrated circuit buffer device, for example bypass elements 2905-2910 in a bypass circuit 2900 as illustrated in FIG. 29.

Write data to larger capacity memory modules is then levelized (in addition to the write data levelization illustrated in logic block 3107) as illustrated by logic block 3112. In an embodiment, additional write delays are added, in response to stored write delay values, to the write data at a master, integrated circuit buffer device and/or memory device. Delays to write data may be selected based on whether write data is transferred through a memory module having an integrated circuit buffer device in a bypass mode of operation. For example, write data provided to memory module 2601 on signal path 2610 from master 2101 may be delayed compared to write data provided to memory module 2601 on signal paths 2612 and 2611 (by way of memory module 2630 b) from master 2101 so that the write data may arrive at approximately the same time.

Signals described herein may be transmitted or received between and within devices/circuits using signal paths and generated using any number of signaling techniques including without limitation, modulating the voltage or current level of an electrical signal. The signals may represent any type of control and timing information (e.g. commands, address values, clock signals, and configuration/parameter information) as well as data. In an embodiment, a signal described herein may be an optical signal.

A variety of signals may be transferred on signal paths as described herein. For example, types of signals include differential (over a pair of signal lines), non-return to zero (“NRZ”), multi-level pulse amplitude modulation (“PAM”), phase shift keying, delay or time modulation, quadrature amplitude modulation (“QAM”) and Trellis coding.

In an embodiment employing multi-level PAM signaling, a data rate may be increased without increasing either the system clock frequency or the number of signal lines by employing multiple voltage levels to encode unique sets of consecutive digital values or symbols. That is, each unique combination of consecutive digital symbols may be assigned to a unique voltage level, or pattern of voltage levels. For example, a 4-level PAM scheme may employ four distinct voltage ranges to distinguish between a pair of consecutive digital values or symbols such as 00, 01, 10 and 11. Here, each voltage range would correspond to one of the unique pairs of consecutive symbols.

In an embodiment, a clock signal is used to synchronize events in a memory module and/or device such as synchronizing receiving and transmitting data and/or control information. In an embodiment, globally synchronous clocking is used (i.e., where a single clock frequency source is distributed to various devices in a memory module/system). In an embodiment, source synchronous clocking is used (i.e., where data is transported alongside a clock signal from a source to a destination such that a clock signal and data become skew tolerant). In an embodiment, encoding data and a clock signal is used. In alternate embodiments, combinations of clocking or synchronization described herein are used.

In embodiments, signal paths described herein include one or more conducting elements, such as a plurality of wires, metal traces (internal or external), signal lines or doped regions (positively or negatively enhanced), as well as one or more optical fibers or optical pathways, singly or in combination. In embodiments, multiple signal paths may replace a single signal path illustrated in the Figures and a single signal path may replace multiple signal paths illustrated in the Figures. In embodiments, a signal path may include a bus and/or point-to-point connection. In an embodiment, signal paths include signal paths for transferring control and data signals. In an alternate embodiment, signal paths include only signals paths for transferring data signals or only signal paths for transferring control signals. In still other embodiments, signal paths transfer unidirectional signals (signals that travel in one direction) or bidirectional signals (signals that travel in two directions) or combinations of both unidirectional and bidirectional signals.

It should be noted that the various circuits disclosed herein may be described using computer aided design tools and expressed (or represented) as data and/or instructions embodied in various computer-readable media, in terms of their behavior, register transfer, logic component, transistor, layout geometries, and/or other characteristics. Formats of files and other objects in which such circuit expressions may be implemented include, but are not limited to: formats supporting behavioral languages such as C, Verilog, and HLDL; formats supporting register level description languages like RTL; formats supporting geometry description languages such as GDSII, GDSIII, GDSIV, CIF, MEBES; and any other suitable formats and languages. Computer-readable media in which such formatted data and/or instructions may be embodied include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media) and carrier waves that may be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media or any combination thereof. Examples of transfers of such formatted data and/or instructions by carrier waves include, but are not limited to, transfers (uploads, downloads, e-mail, etc.) over the Internet and/or other computer networks via one or more data transfer protocols (e.g., HTTP, FTP, SMTP, etc.). When received within a computer system via one or more computer-readable media, such data and/or instruction-based expressions of the above described circuits may be processed by a processing entity (e.g., one or more processors) within the computer system in conjunction with execution of one or more other computer programs including, without limitation, netlist generation programs, place and route programs and the like, to generate a representation or image of a physical manifestation of such circuits. Such representation or image may thereafter be used in device fabrication, for example, by enabling generation of one or more masks that are used to form various components of the circuits in a device fabrication process.

The foregoing description of several embodiments has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to explain inventive principles and practical applications, thereby enabling others skilled in the art to understand various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents. 

1. A system comprising: a master device; a first memory module including, a plurality of integrated circuit memory devices to store first, second and third data, a first integrated circuit buffer device coupled to the plurality of integrated circuit memory devices; a second memory module including a plurality of integrated circuit memory devices to store fourth data, a second integrated circuit buffer device coupled to the plurality of integrated circuit memory devices; a first signal path coupled to the master device and the first integrated circuit buffer device; a second signal path coupled to the first integrated circuit buffer device and the second memory module; a third signal path coupled to the second memory module and the master device; wherein the system is operable in a first and second mode of operation, wherein: during the first mode of operation first data is transferred from the first integrated circuit buffer device to the master on first signal path and fourth data is transferred from the second integrated circuit buffer device to the master on the third signal path; and during the second mode of operation second data is transferred from the first integrated circuit buffer device to the master device on the first signal path and third data is transferred from the first integrated circuit buffer device to the second memory module on the second signal path, and from the second memory module to the master device on the third signal path.
 2. The system of claim 1, wherein the first memory module has a first amount of addressable memory capacity and the second memory module has a second amount of addressable memory capacity, wherein the first amount is different than the second amount.
 3. The system of claim 2, wherein the second and third data are stored at first and second addresses of the first memory module and the second memory module does not have the first and second addresses.
 4. The system of claim 1, wherein the first, second and third signal paths are point-to-point links.
 5. The system of claim 1, wherein the first memory module includes a delay circuit to add a delay in outputting the second data during the second mode of operation, and the second memory module includes a bypass circuit to transfer the third data from the second signal path to the third signal path during the second mode of operation.
 6. The system of claim 5, wherein the delay represents the amount of time for the third data to transfer from the first memory module to the second memory module.
 7. The system of claim 5, wherein the first memory module includes a multiplexer to remove the delay during the first mode of operation.
 8. The system of claim 1, wherein the first memory module includes: an interface having a first interface portion and a second interface portion, wherein the first integrated circuit buffer device transfers data between the plurality of integrated circuit memory devices and the first and second interface portions.
 9. The system of claim 8, further comprising a first socket to connect the interface to the first and second signal paths, and a second socket to connect the second memory module to the second and third signal paths.
 10. The system of claim 8, wherein the plurality of integrated circuit memory devices and the first integrated circuit buffer device in the first memory module are disposed on a substrate and the first interface portion is disposed on a first side of the substrate and the second interface portion is disposed on a second side of the substrate.
 11. A system comprising: a master device; a first memory module to store first data; a second memory module to store second data; a third memory module to store third data; a fourth memory module to store fourth data; a first signal path coupled to the master device and the first memory module; a second signal path coupled to the master device and the second memory module; a third signal path coupled to the master device and the third memory module; a fourth signal path coupled to the master device and the fourth memory module; a fifth signal path coupled to the second and third memory modules; a sixth signal path coupled to the first and fourth memory modules; wherein the system is operable in a first and second mode of operation, wherein: during the first mode of operation the first, second, third and fourth data is transferred from the first, second, third and fourth memory modules to the master device on first, second, third and fourth signal paths; and during the second mode of operation, the first data is transferred from the first memory module to the master device on the first signal path and on the fourth and sixth signal paths by way of the fourth memory module, and the second data is transferred from the second memory module to the master device on the second signal path and on the third and fifth signal paths by way of the third memory module.
 12. The system of claim 11, wherein the first and second memory modules have a first amount of addressable memory capacity and the third and fourth memory modules have a second amount of addressable memory capacity, wherein the first amount is greater than the second amount.
 13. The system of claim 11, wherein the first, second, third and fourth signal paths are point-to-point links.
 14. The system of claim 11, wherein the first memory module includes a delay circuit to add a delay in outputting the first data during the second mode of operation, and the fourth memory module includes a bypass circuit to transfer the first data from the sixth signal path to the fourth signal path during the second mode of operation.
 15. The system of claim 11, wherein the first, second, third and fourth memory modules each includes: a plurality of integrated circuit memory devices; and a plurality of integrated circuit buffer devices coupled to the plurality of integrated circuit memory devices.
 16. A system comprising: a master device to output control information; a first memory module including, a first plurality of integrated circuit memory devices to access stored data in response to the control information, a first plurality of integrated circuit buffer devices coupled to the first plurality of integrated circuit memory devices; a second memory module including, a second plurality of integrated circuit memory devices to access stored data in response to the control information, a second plurality of integrated circuit buffer devices coupled to the second plurality of integrated circuit memory devices; and a first signal path coupled to the master device and the first plurality of integrated circuit buffer devices, the first signal path to provide the control information to the first plurality of integrated circuit buffer devices.
 17. The system of claim 16, further comprising: a first termination disposed on the first memory module and coupled to the first signal path; a second signal path coupled to the master device and the second plurality of integrated circuit buffer devices, the second signal path to provide the control information to the second plurality of integrated circuit buffer devices; and a second termination disposed on the second memory module and coupled to the second signal path.
 18. The system of claim 16, wherein the first signal path includes a first external portion coupled to the master device and the first memory module, a first internal portion disposed on the first memory module, a second external portion coupled to the first memory module and second memory module, and a second internal portion disposed on the second memory module.
 19. The system of claim 16, further comprising: a second signal path to transfer data between the plurality of integrated circuit buffer devices and the master device in response to the control information.
 20. A method of operating a memory system including a master device coupled to a first memory module by a first signal path, the master device coupled to the second memory module by a second signal path, the first and second memory modules coupled by a third signal path, the method comprising: delaying a first read data from the first memory module to the master device based on an amount of time a second data is transferred from the second memory module to the master device; and delaying the first read data from the first memory module to the master device based on the amount of time and an additional amount of time a third data is transferred from the first memory module onto the third signal path and through the second memory module.
 21. The method of claim 20 wherein delaying the first read data from the first memory module to the master device based on the amount of time occurs during a first mode of operation and delaying the first read data from the first memory module to the master device based on the amount of time and the additional amount of time occurs during a second mode of operation.
 22. The method of claim 21, wherein the second data is transferred on the second signal path during the first mode of operation.
 23. The method of claim 22, wherein the first, second and third signal paths are point-to-point links.
 24. The method of claim 20, wherein the first memory module has a different memory capacity than the second memory module.
 25. A system comprising: a master device; a first memory module including, a plurality of integrated circuit memory devices to store first data, a first integrated circuit buffer device coupled to the plurality of integrated circuit memory devices; a second memory module including a plurality of integrated circuit memory devices to store second data, a second integrated circuit buffer device coupled to the plurality of integrated circuit memory devices; a first signal path coupled to the master device and the first integrated circuit buffer device; a second signal path coupled to the first integrated circuit buffer device and the second integrated circuit buffer device; wherein the system is operable in a first and second mode of operation, wherein: during the first mode of operation, the first data is transferred from the first integrated circuit buffer device to the master on the first signal path; and during the second mode of operation, the second data is transferred from the second integrated circuit buffer device to the first integrated circuit buffer device on the second signal path, and from the first integrated circuit buffer device to the master device on the first signal path.
 26. The system of claim 25, wherein the first memory module includes a delay circuit to add a delay in outputting the first data during the first mode of operation.
 27. The system of claim 26, wherein the delay represents at least an amount of time for the second data to transfer from the second memory module to the first memory module.
 28. The system of claim 26, wherein the first memory module includes a select circuit to remove the delay during the second mode of operation.
 29. The system of claim 28, wherein the delay circuit and select circuit are included in the first integrated circuit buffer device.
 30. The system of claim 29, wherein the first integrated circuit buffer device includes a bypass circuit to transfer the second data from a first interface portion of the first memory module to a second interface portion of the first memory module.
 31. A memory module comprising: a plurality of integrated circuit memory devices to store first, second and third data; an integrated circuit buffer device coupled to the plurality of integrated circuit memory devices; an interface having a first interface portion and a second interface portion, wherein the integrated circuit buffer device transfers data between the plurality of integrated circuit memory devices and the first and second interface portions; wherein the memory module is operable in a first and second mode of operation, wherein: during the first mode of operation first data is transferred from the integrated circuit buffer device to the first interface portion; and during the second mode of operation second data is transferred from the first integrated circuit buffer device to the first interface portion and third data is transferred from the first integrated circuit buffer device to the second interface portion.
 32. The memory module of claim 31, wherein the first memory module includes a delay circuit to add a delay in outputting the first data during the second mode of operation.
 33. The memory module of claim 32, wherein the delay represents at least an amount of time for the second data to transfer through another memory module.
 34. The memory module of claim 32, wherein the memory module includes a select circuit to remove the delay during the first mode of operation.
 35. The memory module of claim 34, wherein the delay circuit and select circuit are included in the integrated circuit buffer device.
 36. The memory module of claim 31, including a bypass circuit to transfer a fourth data from the first interface portion to the second interface portion.
 37. The memory module of claim 31, wherein the plurality of integrated circuit memory devices and the first integrated circuit buffer device in the first memory module are disposed on a substrate and the first interface portion is disposed on a first side of the substrate and the second interface portion is disposed on a second side of the substrate.
 38. The memory module of claim 31, wherein the interface includes an edge of a substrate to be positioned into a socket.
 39. A memory system comprising: a master device; a first memory module to store first, second and third data, a second memory module; and means for operating the memory system in a first and second mode of operation, wherein: during the first mode of operation, data is transferred from the first memory module to the master device and from the second memory module to the master device; and during the second mode of operation, data is transferred from the first memory module to the master device and from the first memory module, through the second memory module, and to the master device. 